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Diffstat (limited to 'theories/Reals/Rtrigo1.v')
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diff --git a/theories/Reals/Rtrigo1.v b/theories/Reals/Rtrigo1.v new file mode 100644 index 00000000..6174ef32 --- /dev/null +++ b/theories/Reals/Rtrigo1.v @@ -0,0 +1,1933 @@ +(************************************************************************) +(* v * The Coq Proof Assistant / The Coq Development Team *) +(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2012 *) +(* \VV/ **************************************************************) +(* // * This file is distributed under the terms of the *) +(* * GNU Lesser General Public License Version 2.1 *) +(************************************************************************) + +Require Import Rbase. +Require Import Rfunctions. +Require Import SeqSeries. +Require Export Rtrigo_fun. +Require Export Rtrigo_def. +Require Export Rtrigo_alt. +Require Export Cos_rel. +Require Export Cos_plus. +Require Import ZArith_base. +Require Import Zcomplements. +Require Import Classical_Prop. +Require Import Fourier. +Require Import Ranalysis1. +Require Import Rsqrt_def. +Require Import PSeries_reg. + +Local Open Scope nat_scope. +Local Open Scope R_scope. + +Lemma CVN_R_cos : + forall fn:nat -> R -> R, + fn = (fun (N:nat) (x:R) => (-1) ^ N / INR (fact (2 * N)) * x ^ (2 * N)) -> + CVN_R fn. +Proof. + unfold CVN_R in |- *; intros. + cut ((r:R) <> 0). + intro hyp_r; unfold CVN_r in |- *. + exists (fun n:nat => / INR (fact (2 * n)) * r ^ (2 * n)). + cut + { l:R | + Un_cv + (fun n:nat => + sum_f_R0 (fun k:nat => Rabs (/ INR (fact (2 * k)) * r ^ (2 * k))) + n) l }. + intro X; elim X; intros. + exists x. + split. + apply p. + intros; rewrite H; unfold Rdiv in |- *; do 2 rewrite Rabs_mult. + rewrite pow_1_abs; rewrite Rmult_1_l. + cut (0 < / INR (fact (2 * n))). + intro; rewrite (Rabs_right _ (Rle_ge _ _ (Rlt_le _ _ H1))). + apply Rmult_le_compat_l. + left; apply H1. + rewrite <- RPow_abs; apply pow_maj_Rabs. + rewrite Rabs_Rabsolu. + unfold Boule in H0; rewrite Rminus_0_r in H0. + left; apply H0. + apply Rinv_0_lt_compat; apply INR_fact_lt_0. + apply Alembert_C2. + intro; apply Rabs_no_R0. + apply prod_neq_R0. + apply Rinv_neq_0_compat. + apply INR_fact_neq_0. + apply pow_nonzero; assumption. + assert (H0 := Alembert_cos). + unfold cos_n in H0; unfold Un_cv in H0; unfold Un_cv in |- *; intros. + cut (0 < eps / Rsqr r). + intro; elim (H0 _ H2); intros N0 H3. + exists N0; intros. + unfold R_dist in |- *; assert (H5 := H3 _ H4). + unfold R_dist in H5; + replace + (Rabs + (Rabs (/ INR (fact (2 * S n)) * r ^ (2 * S n)) / + Rabs (/ INR (fact (2 * n)) * r ^ (2 * n)))) with + (Rsqr r * + Rabs ((-1) ^ S n / INR (fact (2 * S n)) / ((-1) ^ n / INR (fact (2 * n))))). + apply Rmult_lt_reg_l with (/ Rsqr r). + apply Rinv_0_lt_compat; apply Rsqr_pos_lt; assumption. + pattern (/ Rsqr r) at 1 in |- *; replace (/ Rsqr r) with (Rabs (/ Rsqr r)). + rewrite <- Rabs_mult; rewrite Rmult_minus_distr_l; rewrite Rmult_0_r; + rewrite <- Rmult_assoc; rewrite <- Rinv_l_sym. + rewrite Rmult_1_l; rewrite <- (Rmult_comm eps); apply H5. + unfold Rsqr in |- *; apply prod_neq_R0; assumption. + rewrite Rabs_Rinv. + rewrite Rabs_right. + reflexivity. + apply Rle_ge; apply Rle_0_sqr. + unfold Rsqr in |- *; apply prod_neq_R0; assumption. + rewrite (Rmult_comm (Rsqr r)); unfold Rdiv in |- *; repeat rewrite Rabs_mult; + rewrite Rabs_Rabsolu; rewrite pow_1_abs; rewrite Rmult_1_l; + repeat rewrite Rmult_assoc; apply Rmult_eq_compat_l. + rewrite Rabs_Rinv. + rewrite Rabs_mult; rewrite (pow_1_abs n); rewrite Rmult_1_l; + rewrite <- Rabs_Rinv. + rewrite Rinv_involutive. + rewrite Rinv_mult_distr. + rewrite Rabs_Rinv. + rewrite Rinv_involutive. + rewrite (Rmult_comm (Rabs (Rabs (r ^ (2 * S n))))); rewrite Rabs_mult; + rewrite Rabs_Rabsolu; rewrite Rmult_assoc; apply Rmult_eq_compat_l. + rewrite Rabs_Rinv. + do 2 rewrite Rabs_Rabsolu; repeat rewrite Rabs_right. + replace (r ^ (2 * S n)) with (r ^ (2 * n) * r * r). + repeat rewrite <- Rmult_assoc; rewrite <- Rinv_l_sym. + unfold Rsqr in |- *; ring. + apply pow_nonzero; assumption. + replace (2 * S n)%nat with (S (S (2 * n))). + simpl in |- *; ring. + ring. + apply Rle_ge; apply pow_le; left; apply (cond_pos r). + apply Rle_ge; apply pow_le; left; apply (cond_pos r). + apply Rabs_no_R0; apply pow_nonzero; assumption. + apply Rabs_no_R0; apply INR_fact_neq_0. + apply INR_fact_neq_0. + apply Rabs_no_R0; apply Rinv_neq_0_compat; apply INR_fact_neq_0. + apply Rabs_no_R0; apply pow_nonzero; assumption. + apply INR_fact_neq_0. + apply Rinv_neq_0_compat; apply INR_fact_neq_0. + apply prod_neq_R0. + apply pow_nonzero; discrR. + apply Rinv_neq_0_compat; apply INR_fact_neq_0. + unfold Rdiv in |- *; apply Rmult_lt_0_compat. + apply H1. + apply Rinv_0_lt_compat; apply Rsqr_pos_lt; assumption. + assert (H0 := cond_pos r); red in |- *; intro; rewrite H1 in H0; + elim (Rlt_irrefl _ H0). +Qed. + +(**********) +Lemma continuity_cos : continuity cos. +Proof. + set (fn := fun (N:nat) (x:R) => (-1) ^ N / INR (fact (2 * N)) * x ^ (2 * N)). + cut (CVN_R fn). + intro; cut (forall x:R, { l:R | Un_cv (fun N:nat => SP fn N x) l }). + intro cv; cut (forall n:nat, continuity (fn n)). + intro; cut (forall x:R, cos x = SFL fn cv x). + intro; cut (continuity (SFL fn cv) -> continuity cos). + intro; apply H1. + apply SFL_continuity; assumption. + unfold continuity in |- *; unfold continuity_pt in |- *; + unfold continue_in in |- *; unfold limit1_in in |- *; + unfold limit_in in |- *; simpl in |- *; unfold R_dist in |- *; + intros. + elim (H1 x _ H2); intros. + exists x0; intros. + elim H3; intros. + split. + apply H4. + intros; rewrite (H0 x); rewrite (H0 x1); apply H5; apply H6. + intro; unfold cos, SFL in |- *. + case (cv x); case (exist_cos (Rsqr x)); intros. + symmetry in |- *; eapply UL_sequence. + apply u. + unfold cos_in in c; unfold infinite_sum in c; unfold Un_cv in |- *; intros. + elim (c _ H0); intros N0 H1. + exists N0; intros. + unfold R_dist in H1; unfold R_dist, SP in |- *. + replace (sum_f_R0 (fun k:nat => fn k x) n) with + (sum_f_R0 (fun i:nat => cos_n i * Rsqr x ^ i) n). + apply H1; assumption. + apply sum_eq; intros. + unfold cos_n, fn in |- *; apply Rmult_eq_compat_l. + unfold Rsqr in |- *; rewrite pow_sqr; reflexivity. + intro; unfold fn in |- *; + replace (fun x:R => (-1) ^ n / INR (fact (2 * n)) * x ^ (2 * n)) with + (fct_cte ((-1) ^ n / INR (fact (2 * n))) * pow_fct (2 * n))%F; + [ idtac | reflexivity ]. + apply continuity_mult. + apply derivable_continuous; apply derivable_const. + apply derivable_continuous; apply (derivable_pow (2 * n)). + apply CVN_R_CVS; apply X. + apply CVN_R_cos; unfold fn in |- *; reflexivity. +Qed. + +Lemma sin_gt_cos_7_8 : sin (7 / 8) > cos (7 / 8). +Proof. +assert (lo1 : 0 <= 7/8) by fourier. +assert (up1 : 7/8 <= 4) by fourier. +assert (lo : -2 <= 7/8) by fourier. +assert (up : 7/8 <= 2) by fourier. +destruct (pre_sin_bound _ 0 lo1 up1) as [lower _ ]. +destruct (pre_cos_bound _ 0 lo up) as [_ upper]. +apply Rle_lt_trans with (1 := upper). +apply Rlt_le_trans with (2 := lower). +unfold cos_approx, sin_approx. +simpl sum_f_R0; replace 7 with (IZR 7) by (simpl; field). +replace 8 with (IZR 8) by (simpl; field). +unfold cos_term, sin_term; simpl fact; rewrite !INR_IZR_INZ. +simpl plus; simpl mult. +field_simplify; + try (repeat apply conj; apply not_eq_sym, Rlt_not_eq, (IZR_lt 0); reflexivity). +unfold Rminus; rewrite !pow_IZR, <- !mult_IZR, <- !opp_IZR, <- ?plus_IZR. +match goal with + |- IZR ?a / ?b < ?c / ?d => + apply Rmult_lt_reg_r with d;[apply (IZR_lt 0); reflexivity | + unfold Rdiv at 2; rewrite Rmult_assoc, Rinv_l, Rmult_1_r, Rmult_comm; + [ |apply not_eq_sym, Rlt_not_eq, (IZR_lt 0); reflexivity ]]; + apply Rmult_lt_reg_r with b;[apply (IZR_lt 0); reflexivity | ] +end. +unfold Rdiv; rewrite !Rmult_assoc, Rinv_l, Rmult_1_r; + [ | apply not_eq_sym, Rlt_not_eq, (IZR_lt 0); reflexivity]. +repeat (rewrite <- !plus_IZR || rewrite <- !mult_IZR). +apply IZR_lt; reflexivity. +Qed. + +Definition PI_2_aux : {z | 7/8 <= z <= 7/4 /\ -cos z = 0}. +assert (cc : continuity (fun r =>- cos r)). + apply continuity_opp, continuity_cos. +assert (cvp : 0 < cos (7/8)). + assert (int78 : -2 <= 7/8 <= 2) by (split; fourier). + destruct int78 as [lower upper]. + case (pre_cos_bound _ 0 lower upper). + unfold cos_approx; simpl sum_f_R0; unfold cos_term. + intros cl _; apply Rlt_le_trans with (2 := cl); simpl. + fourier. +assert (cun : cos (7/4) < 0). + replace (7/4) with (7/8 + 7/8) by field. + rewrite cos_plus. + apply Rlt_minus; apply Rsqr_incrst_1. + exact sin_gt_cos_7_8. + apply Rlt_le; assumption. + apply Rlt_le; apply Rlt_trans with (1 := cvp); exact sin_gt_cos_7_8. +apply IVT; auto; fourier. +Qed. + +Definition PI2 := proj1_sig PI_2_aux. + +Definition PI := 2 * PI2. + +Lemma cos_pi2 : cos PI2 = 0. +unfold PI2; case PI_2_aux; simpl. +intros x [_ q]; rewrite <- (Ropp_involutive (cos x)), q; apply Ropp_0. +Qed. + +Lemma pi2_int : 7/8 <= PI2 <= 7/4. +unfold PI2; case PI_2_aux; simpl; tauto. +Qed. + +(**********) +Lemma cos_minus : forall x y:R, cos (x - y) = cos x * cos y + sin x * sin y. +Proof. + intros; unfold Rminus in |- *; rewrite cos_plus. + rewrite <- cos_sym; rewrite sin_antisym; ring. +Qed. + +(**********) +Lemma sin2_cos2 : forall x:R, Rsqr (sin x) + Rsqr (cos x) = 1. +Proof. + intro; unfold Rsqr in |- *; rewrite Rplus_comm; rewrite <- (cos_minus x x); + unfold Rminus in |- *; rewrite Rplus_opp_r; apply cos_0. +Qed. + +Lemma cos2 : forall x:R, Rsqr (cos x) = 1 - Rsqr (sin x). +Proof. + intros x; rewrite <- (sin2_cos2 x); ring. +Qed. + +Lemma sin2 : forall x:R, Rsqr (sin x) = 1 - Rsqr (cos x). +Proof. + intro x; generalize (cos2 x); intro H1; rewrite H1. + unfold Rminus in |- *; rewrite Ropp_plus_distr; rewrite <- Rplus_assoc; + rewrite Rplus_opp_r; rewrite Rplus_0_l; symmetry in |- *; + apply Ropp_involutive. +Qed. + +(**********) +Lemma cos_PI2 : cos (PI / 2) = 0. +Proof. + unfold PI; generalize cos_pi2; replace ((2 * PI2)/2) with PI2 by field; tauto. +Qed. + +Lemma sin_pos_tech : forall x, 0 < x < 2 -> 0 < sin x. +intros x [int1 int2]. +assert (lo : 0 <= x) by (apply Rlt_le; assumption). +assert (up : x <= 4) by (apply Rlt_le, Rlt_trans with (1:=int2); fourier). +destruct (pre_sin_bound _ 0 lo up) as [t _]; clear lo up. +apply Rlt_le_trans with (2:= t); clear t. +unfold sin_approx; simpl sum_f_R0; unfold sin_term; simpl. +match goal with |- _ < ?a => + replace a with (x * (1 - x^2/6)) by (simpl; field) +end. +assert (t' : x ^ 2 <= 4). + replace 4 with (2 ^ 2) by field. + apply (pow_incr x 2); split; apply Rlt_le; assumption. +apply Rmult_lt_0_compat;[assumption | fourier ]. +Qed. + +Lemma sin_PI2 : sin (PI / 2) = 1. +replace (PI / 2) with PI2 by (unfold PI; field). +assert (int' : 0 < PI2 < 2). + destruct pi2_int; split; fourier. +assert (lo2 := sin_pos_tech PI2 int'). +assert (t2 : Rabs (sin PI2) = 1). + rewrite <- Rabs_R1; apply Rsqr_eq_abs_0. + rewrite Rsqr_1, sin2, cos_pi2, Rsqr_0, Rminus_0_r; reflexivity. +revert t2; rewrite Rabs_pos_eq;[| apply Rlt_le]; tauto. +Qed. + +Lemma PI_RGT_0 : PI > 0. +Proof. unfold PI; destruct pi2_int; fourier. Qed. + +Lemma PI_4 : PI <= 4. +Proof. unfold PI; destruct pi2_int; fourier. Qed. + +(**********) +Lemma PI_neq0 : PI <> 0. +Proof. + red in |- *; intro; assert (H0 := PI_RGT_0); rewrite H in H0; + elim (Rlt_irrefl _ H0). +Qed. + + +(**********) +Lemma cos_PI : cos PI = -1. +Proof. + replace PI with (PI / 2 + PI / 2). + rewrite cos_plus. + rewrite sin_PI2; rewrite cos_PI2. + ring. + symmetry in |- *; apply double_var. +Qed. + +Lemma sin_PI : sin PI = 0. +Proof. + assert (H := sin2_cos2 PI). + rewrite cos_PI in H. + rewrite <- Rsqr_neg in H. + rewrite Rsqr_1 in H. + cut (Rsqr (sin PI) = 0). + intro; apply (Rsqr_eq_0 _ H0). + apply Rplus_eq_reg_l with 1. + rewrite Rplus_0_r; rewrite Rplus_comm; exact H. +Qed. + +Lemma sin_bound : forall (a : R) (n : nat), 0 <= a -> a <= PI -> + sin_approx a (2 * n + 1) <= sin a <= sin_approx a (2 * (n + 1)). +Proof. +intros a n a0 api; apply pre_sin_bound. + assumption. +apply Rle_trans with (1:= api) (2 := PI_4). +Qed. + +Lemma cos_bound : forall (a : R) (n : nat), - PI / 2 <= a -> a <= PI / 2 -> + cos_approx a (2 * n + 1) <= cos a <= cos_approx a (2 * (n + 1)). +Proof. +intros a n lower upper; apply pre_cos_bound. + apply Rle_trans with (2 := lower). + apply Rmult_le_reg_r with 2; [fourier |]. + replace ((-PI/2) * 2) with (-PI) by field. + assert (t := PI_4); fourier. +apply Rle_trans with (1 := upper). +apply Rmult_le_reg_r with 2; [fourier | ]. +replace ((PI/2) * 2) with PI by field. +generalize PI_4; intros; fourier. +Qed. +(**********) +Lemma neg_cos : forall x:R, cos (x + PI) = - cos x. +Proof. + intro x; rewrite cos_plus; rewrite sin_PI; rewrite cos_PI; ring. +Qed. + +(**********) +Lemma sin_cos : forall x:R, sin x = - cos (PI / 2 + x). +Proof. + intro x; rewrite cos_plus; rewrite sin_PI2; rewrite cos_PI2; ring. +Qed. + +(**********) +Lemma sin_plus : forall x y:R, sin (x + y) = sin x * cos y + cos x * sin y. +Proof. + intros. + rewrite (sin_cos (x + y)). + replace (PI / 2 + (x + y)) with (PI / 2 + x + y); [ rewrite cos_plus | ring ]. + rewrite (sin_cos (PI / 2 + x)). + replace (PI / 2 + (PI / 2 + x)) with (x + PI). + rewrite neg_cos. + replace (cos (PI / 2 + x)) with (- sin x). + ring. + rewrite sin_cos; rewrite Ropp_involutive; reflexivity. + pattern PI at 1 in |- *; rewrite (double_var PI); ring. +Qed. + +Lemma sin_minus : forall x y:R, sin (x - y) = sin x * cos y - cos x * sin y. +Proof. + intros; unfold Rminus in |- *; rewrite sin_plus. + rewrite <- cos_sym; rewrite sin_antisym; ring. +Qed. + +(**********) +Definition tan (x:R) : R := sin x / cos x. + +Lemma tan_plus : + forall x y:R, + cos x <> 0 -> + cos y <> 0 -> + cos (x + y) <> 0 -> + 1 - tan x * tan y <> 0 -> + tan (x + y) = (tan x + tan y) / (1 - tan x * tan y). +Proof. + intros; unfold tan in |- *; rewrite sin_plus; rewrite cos_plus; + unfold Rdiv in |- *; + replace (cos x * cos y - sin x * sin y) with + (cos x * cos y * (1 - sin x * / cos x * (sin y * / cos y))). + rewrite Rinv_mult_distr. + repeat rewrite <- Rmult_assoc; + replace ((sin x * cos y + cos x * sin y) * / (cos x * cos y)) with + (sin x * / cos x + sin y * / cos y). + reflexivity. + rewrite Rmult_plus_distr_r; rewrite Rinv_mult_distr. + repeat rewrite Rmult_assoc; repeat rewrite (Rmult_comm (sin x)); + repeat rewrite <- Rmult_assoc. + repeat rewrite Rinv_r_simpl_m; [ reflexivity | assumption | assumption ]. + assumption. + assumption. + apply prod_neq_R0; assumption. + assumption. + unfold Rminus in |- *; rewrite Rmult_plus_distr_l; rewrite Rmult_1_r; + apply Rplus_eq_compat_l; repeat rewrite Rmult_assoc; + rewrite (Rmult_comm (sin x)); rewrite (Rmult_comm (cos y)); + rewrite <- Ropp_mult_distr_r_reverse; repeat rewrite <- Rmult_assoc; + rewrite <- Rinv_r_sym. + rewrite Rmult_1_l; rewrite (Rmult_comm (sin x)); + rewrite <- Ropp_mult_distr_r_reverse; repeat rewrite Rmult_assoc; + apply Rmult_eq_compat_l; rewrite (Rmult_comm (/ cos y)); + rewrite Rmult_assoc; rewrite <- Rinv_r_sym. + apply Rmult_1_r. + assumption. + assumption. +Qed. + +(*******************************************************) +(** * Some properties of cos, sin and tan *) +(*******************************************************) + +Lemma sin_2a : forall x:R, sin (2 * x) = 2 * sin x * cos x. +Proof. + intro x; rewrite double; rewrite sin_plus. + rewrite <- (Rmult_comm (sin x)); symmetry in |- *; rewrite Rmult_assoc; + apply double. +Qed. + +Lemma cos_2a : forall x:R, cos (2 * x) = cos x * cos x - sin x * sin x. +Proof. + intro x; rewrite double; apply cos_plus. +Qed. + +Lemma cos_2a_cos : forall x:R, cos (2 * x) = 2 * cos x * cos x - 1. +Proof. + intro x; rewrite double; unfold Rminus in |- *; rewrite Rmult_assoc; + rewrite cos_plus; generalize (sin2_cos2 x); rewrite double; + intro H1; rewrite <- H1; ring_Rsqr. +Qed. + +Lemma cos_2a_sin : forall x:R, cos (2 * x) = 1 - 2 * sin x * sin x. +Proof. + intro x; rewrite Rmult_assoc; unfold Rminus in |- *; repeat rewrite double. + generalize (sin2_cos2 x); intro H1; rewrite <- H1; rewrite cos_plus; + ring_Rsqr. +Qed. + +Lemma tan_2a : + forall x:R, + cos x <> 0 -> + cos (2 * x) <> 0 -> + 1 - tan x * tan x <> 0 -> tan (2 * x) = 2 * tan x / (1 - tan x * tan x). +Proof. + repeat rewrite double; intros; repeat rewrite double; rewrite double in H0; + apply tan_plus; assumption. +Qed. + +Lemma sin_neg : forall x:R, sin (- x) = - sin x. +Proof. + apply sin_antisym. +Qed. + +Lemma cos_neg : forall x:R, cos (- x) = cos x. +Proof. + intro; symmetry in |- *; apply cos_sym. +Qed. + +Lemma tan_0 : tan 0 = 0. +Proof. + unfold tan in |- *; rewrite sin_0; rewrite cos_0. + unfold Rdiv in |- *; apply Rmult_0_l. +Qed. + +Lemma tan_neg : forall x:R, tan (- x) = - tan x. +Proof. + intros x; unfold tan in |- *; rewrite sin_neg; rewrite cos_neg; + unfold Rdiv in |- *. + apply Ropp_mult_distr_l_reverse. +Qed. + +Lemma tan_minus : + forall x y:R, + cos x <> 0 -> + cos y <> 0 -> + cos (x - y) <> 0 -> + 1 + tan x * tan y <> 0 -> + tan (x - y) = (tan x - tan y) / (1 + tan x * tan y). +Proof. + intros; unfold Rminus in |- *; rewrite tan_plus. + rewrite tan_neg; unfold Rminus in |- *; rewrite <- Ropp_mult_distr_l_reverse; + rewrite Rmult_opp_opp; reflexivity. + assumption. + rewrite cos_neg; assumption. + assumption. + rewrite tan_neg; unfold Rminus in |- *; rewrite <- Ropp_mult_distr_l_reverse; + rewrite Rmult_opp_opp; assumption. +Qed. + +Lemma cos_3PI2 : cos (3 * (PI / 2)) = 0. +Proof. + replace (3 * (PI / 2)) with (PI + PI / 2). + rewrite cos_plus; rewrite sin_PI; rewrite cos_PI2; ring. + pattern PI at 1 in |- *; rewrite (double_var PI). + ring. +Qed. + +Lemma sin_2PI : sin (2 * PI) = 0. +Proof. + rewrite sin_2a; rewrite sin_PI; ring. +Qed. + +Lemma cos_2PI : cos (2 * PI) = 1. +Proof. + rewrite cos_2a; rewrite sin_PI; rewrite cos_PI; ring. +Qed. + +Lemma neg_sin : forall x:R, sin (x + PI) = - sin x. +Proof. + intro x; rewrite sin_plus; rewrite sin_PI; rewrite cos_PI; ring. +Qed. + +Lemma sin_PI_x : forall x:R, sin (PI - x) = sin x. +Proof. + intro x; rewrite sin_minus; rewrite sin_PI; rewrite cos_PI; rewrite Rmult_0_l; + unfold Rminus in |- *; rewrite Rplus_0_l; rewrite Ropp_mult_distr_l_reverse; + rewrite Ropp_involutive; apply Rmult_1_l. +Qed. + +Lemma sin_period : forall (x:R) (k:nat), sin (x + 2 * INR k * PI) = sin x. +Proof. + intros x k; induction k as [| k Hreck]. + simpl in |- *; ring_simplify (x + 2 * 0 * PI). + trivial. + + replace (x + 2 * INR (S k) * PI) with (x + 2 * INR k * PI + 2 * PI). + rewrite sin_plus in |- *; rewrite sin_2PI in |- *; rewrite cos_2PI in |- *. + ring_simplify; trivial. + rewrite S_INR in |- *; ring. +Qed. + +Lemma cos_period : forall (x:R) (k:nat), cos (x + 2 * INR k * PI) = cos x. +Proof. + intros x k; induction k as [| k Hreck]. + simpl in |- *; ring_simplify (x + 2 * 0 * PI). + trivial. + + replace (x + 2 * INR (S k) * PI) with (x + 2 * INR k * PI + 2 * PI). + rewrite cos_plus in |- *; rewrite sin_2PI in |- *; rewrite cos_2PI in |- *. + ring_simplify; trivial. + rewrite S_INR in |- *; ring. +Qed. + +Lemma sin_shift : forall x:R, sin (PI / 2 - x) = cos x. +Proof. + intro x; rewrite sin_minus; rewrite sin_PI2; rewrite cos_PI2; ring. +Qed. + +Lemma cos_shift : forall x:R, cos (PI / 2 - x) = sin x. +Proof. + intro x; rewrite cos_minus; rewrite sin_PI2; rewrite cos_PI2; ring. +Qed. + +Lemma cos_sin : forall x:R, cos x = sin (PI / 2 + x). +Proof. + intro x; rewrite sin_plus; rewrite sin_PI2; rewrite cos_PI2; ring. +Qed. + +Lemma PI2_RGT_0 : 0 < PI / 2. +Proof. + unfold Rdiv in |- *; apply Rmult_lt_0_compat; + [ apply PI_RGT_0 | apply Rinv_0_lt_compat; prove_sup ]. +Qed. + +Lemma SIN_bound : forall x:R, -1 <= sin x <= 1. +Proof. + intro; case (Rle_dec (-1) (sin x)); intro. + case (Rle_dec (sin x) 1); intro. + split; assumption. + cut (1 < sin x). + intro; + generalize + (Rsqr_incrst_1 1 (sin x) H (Rlt_le 0 1 Rlt_0_1) + (Rlt_le 0 (sin x) (Rlt_trans 0 1 (sin x) Rlt_0_1 H))); + rewrite Rsqr_1; intro; rewrite sin2 in H0; unfold Rminus in H0; + generalize (Rplus_lt_compat_l (-1) 1 (1 + - Rsqr (cos x)) H0); + repeat rewrite <- Rplus_assoc; repeat rewrite Rplus_opp_l; + rewrite Rplus_0_l; intro; rewrite <- Ropp_0 in H1; + generalize (Ropp_lt_gt_contravar (-0) (- Rsqr (cos x)) H1); + repeat rewrite Ropp_involutive; intro; generalize (Rle_0_sqr (cos x)); + intro; elim (Rlt_irrefl 0 (Rle_lt_trans 0 (Rsqr (cos x)) 0 H3 H2)). + auto with real. + cut (sin x < -1). + intro; generalize (Ropp_lt_gt_contravar (sin x) (-1) H); + rewrite Ropp_involutive; clear H; intro; + generalize + (Rsqr_incrst_1 1 (- sin x) H (Rlt_le 0 1 Rlt_0_1) + (Rlt_le 0 (- sin x) (Rlt_trans 0 1 (- sin x) Rlt_0_1 H))); + rewrite Rsqr_1; intro; rewrite <- Rsqr_neg in H0; + rewrite sin2 in H0; unfold Rminus in H0; + generalize (Rplus_lt_compat_l (-1) 1 (1 + - Rsqr (cos x)) H0); + repeat rewrite <- Rplus_assoc; repeat rewrite Rplus_opp_l; + rewrite Rplus_0_l; intro; rewrite <- Ropp_0 in H1; + generalize (Ropp_lt_gt_contravar (-0) (- Rsqr (cos x)) H1); + repeat rewrite Ropp_involutive; intro; generalize (Rle_0_sqr (cos x)); + intro; elim (Rlt_irrefl 0 (Rle_lt_trans 0 (Rsqr (cos x)) 0 H3 H2)). + auto with real. +Qed. + +Lemma COS_bound : forall x:R, -1 <= cos x <= 1. +Proof. + intro; rewrite <- sin_shift; apply SIN_bound. +Qed. + +Lemma cos_sin_0 : forall x:R, ~ (cos x = 0 /\ sin x = 0). +Proof. + intro; red in |- *; intro; elim H; intros; generalize (sin2_cos2 x); intro; + rewrite H0 in H2; rewrite H1 in H2; repeat rewrite Rsqr_0 in H2; + rewrite Rplus_0_r in H2; generalize Rlt_0_1; intro; + rewrite <- H2 in H3; elim (Rlt_irrefl 0 H3). +Qed. + +Lemma cos_sin_0_var : forall x:R, cos x <> 0 \/ sin x <> 0. +Proof. + intros x. + destruct (Req_dec (cos x) 0). 2: now left. + right. intros H'. + apply (cos_sin_0 x). + now split. +Qed. + +(*****************************************************************) +(** * Using series definitions of cos and sin *) +(*****************************************************************) + +Definition sin_lb (a:R) : R := sin_approx a 3. +Definition sin_ub (a:R) : R := sin_approx a 4. +Definition cos_lb (a:R) : R := cos_approx a 3. +Definition cos_ub (a:R) : R := cos_approx a 4. + +Lemma sin_lb_gt_0 : forall a:R, 0 < a -> a <= PI / 2 -> 0 < sin_lb a. +Proof. + intros. + unfold sin_lb in |- *; unfold sin_approx in |- *; unfold sin_term in |- *. + set (Un := fun i:nat => a ^ (2 * i + 1) / INR (fact (2 * i + 1))). + replace + (sum_f_R0 + (fun i:nat => (-1) ^ i * (a ^ (2 * i + 1) / INR (fact (2 * i + 1)))) 3) + with (sum_f_R0 (fun i:nat => (-1) ^ i * Un i) 3); + [ idtac | apply sum_eq; intros; unfold Un in |- *; reflexivity ]. + cut (forall n:nat, Un (S n) < Un n). + intro; simpl in |- *. + repeat rewrite Rmult_1_l; repeat rewrite Rmult_1_r; + replace (-1 * Un 1%nat) with (- Un 1%nat); [ idtac | ring ]; + replace (-1 * -1 * Un 2%nat) with (Un 2%nat); [ idtac | ring ]; + replace (-1 * (-1 * -1) * Un 3%nat) with (- Un 3%nat); + [ idtac | ring ]; + replace (Un 0%nat + - Un 1%nat + Un 2%nat + - Un 3%nat) with + (Un 0%nat - Un 1%nat + (Un 2%nat - Un 3%nat)); [ idtac | ring ]. + apply Rplus_lt_0_compat. + unfold Rminus in |- *; apply Rplus_lt_reg_r with (Un 1%nat); + rewrite Rplus_0_r; rewrite (Rplus_comm (Un 1%nat)); + rewrite Rplus_assoc; rewrite Rplus_opp_l; rewrite Rplus_0_r; + apply H1. + unfold Rminus in |- *; apply Rplus_lt_reg_r with (Un 3%nat); + rewrite Rplus_0_r; rewrite (Rplus_comm (Un 3%nat)); + rewrite Rplus_assoc; rewrite Rplus_opp_l; rewrite Rplus_0_r; + apply H1. + intro; unfold Un in |- *. + cut ((2 * S n + 1)%nat = (2 * n + 1 + 2)%nat). + intro; rewrite H1. + rewrite pow_add; unfold Rdiv in |- *; rewrite Rmult_assoc; + apply Rmult_lt_compat_l. + apply pow_lt; assumption. + rewrite <- H1; apply Rmult_lt_reg_l with (INR (fact (2 * n + 1))). + apply lt_INR_0; apply neq_O_lt. + assert (H2 := fact_neq_0 (2 * n + 1)). + red in |- *; intro; elim H2; symmetry in |- *; assumption. + rewrite <- Rinv_r_sym. + apply Rmult_lt_reg_l with (INR (fact (2 * S n + 1))). + apply lt_INR_0; apply neq_O_lt. + assert (H2 := fact_neq_0 (2 * S n + 1)). + red in |- *; intro; elim H2; symmetry in |- *; assumption. + rewrite (Rmult_comm (INR (fact (2 * S n + 1)))); repeat rewrite Rmult_assoc; + rewrite <- Rinv_l_sym. + do 2 rewrite Rmult_1_r; apply Rle_lt_trans with (INR (fact (2 * n + 1)) * 4). + apply Rmult_le_compat_l. + replace 0 with (INR 0); [ idtac | reflexivity ]; apply le_INR; apply le_O_n. + simpl in |- *; rewrite Rmult_1_r; replace 4 with (Rsqr 2); + [ idtac | ring_Rsqr ]; replace (a * a) with (Rsqr a); + [ idtac | reflexivity ]; apply Rsqr_incr_1. + apply Rle_trans with (PI / 2); + [ assumption + | unfold Rdiv in |- *; apply Rmult_le_reg_l with 2; + [ prove_sup0 + | rewrite <- Rmult_assoc; rewrite Rinv_r_simpl_m; + [ replace 4 with 4; [ apply PI_4 | ring ] | discrR ] ] ]. + left; assumption. + left; prove_sup0. + rewrite H1; replace (2 * n + 1 + 2)%nat with (S (S (2 * n + 1))). + do 2 rewrite fact_simpl; do 2 rewrite mult_INR. + repeat rewrite <- Rmult_assoc. + rewrite <- (Rmult_comm (INR (fact (2 * n + 1)))). + rewrite Rmult_assoc. + apply Rmult_lt_compat_l. + apply lt_INR_0; apply neq_O_lt. + assert (H2 := fact_neq_0 (2 * n + 1)). + red in |- *; intro; elim H2; symmetry in |- *; assumption. + do 2 rewrite S_INR; rewrite plus_INR; rewrite mult_INR; set (x := INR n); + unfold INR in |- *. + replace ((2 * x + 1 + 1 + 1) * (2 * x + 1 + 1)) with (4 * x * x + 10 * x + 6); + [ idtac | ring ]. + apply Rplus_lt_reg_r with (-4); rewrite Rplus_opp_l; + replace (-4 + (4 * x * x + 10 * x + 6)) with (4 * x * x + 10 * x + 2); + [ idtac | ring ]. + apply Rplus_le_lt_0_compat. + cut (0 <= x). + intro; apply Rplus_le_le_0_compat; repeat apply Rmult_le_pos; + assumption || left; prove_sup. + unfold x in |- *; replace 0 with (INR 0); + [ apply le_INR; apply le_O_n | reflexivity ]. + prove_sup0. + ring. + apply INR_fact_neq_0. + apply INR_fact_neq_0. + ring. +Qed. + +Lemma SIN : forall a:R, 0 <= a -> a <= PI -> sin_lb a <= sin a <= sin_ub a. + intros; unfold sin_lb, sin_ub in |- *; apply (sin_bound a 1 H H0). +Qed. + +Lemma COS : + forall a:R, - PI / 2 <= a -> a <= PI / 2 -> cos_lb a <= cos a <= cos_ub a. + intros; unfold cos_lb, cos_ub in |- *; apply (cos_bound a 1 H H0). +Qed. + +(**********) +Lemma _PI2_RLT_0 : - (PI / 2) < 0. +Proof. + rewrite <- Ropp_0; apply Ropp_lt_contravar; apply PI2_RGT_0. +Qed. + +Lemma PI4_RLT_PI2 : PI / 4 < PI / 2. +Proof. + unfold Rdiv in |- *; apply Rmult_lt_compat_l. + apply PI_RGT_0. + apply Rinv_lt_contravar. + apply Rmult_lt_0_compat; prove_sup0. + pattern 2 at 1 in |- *; rewrite <- Rplus_0_r. + replace 4 with (2 + 2); [ apply Rplus_lt_compat_l; prove_sup0 | ring ]. +Qed. + +Lemma PI2_Rlt_PI : PI / 2 < PI. +Proof. + unfold Rdiv in |- *; pattern PI at 2 in |- *; rewrite <- Rmult_1_r. + apply Rmult_lt_compat_l. + apply PI_RGT_0. + pattern 1 at 3 in |- *; rewrite <- Rinv_1; apply Rinv_lt_contravar. + rewrite Rmult_1_l; prove_sup0. + pattern 1 at 1 in |- *; rewrite <- Rplus_0_r; apply Rplus_lt_compat_l; + apply Rlt_0_1. +Qed. + +(***************************************************) +(** * Increasing and decreasing of [cos] and [sin] *) +(***************************************************) +Theorem sin_gt_0 : forall x:R, 0 < x -> x < PI -> 0 < sin x. +Proof. + intros; elim (SIN x (Rlt_le 0 x H) (Rlt_le x PI H0)); intros H1 _; + case (Rtotal_order x (PI / 2)); intro H2. + apply Rlt_le_trans with (sin_lb x). + apply sin_lb_gt_0; [ assumption | left; assumption ]. + assumption. + elim H2; intro H3. + rewrite H3; rewrite sin_PI2; apply Rlt_0_1. + rewrite <- sin_PI_x; generalize (Ropp_gt_lt_contravar x (PI / 2) H3); + intro H4; generalize (Rplus_lt_compat_l PI (- x) (- (PI / 2)) H4). + replace (PI + - x) with (PI - x). + replace (PI + - (PI / 2)) with (PI / 2). + intro H5; generalize (Ropp_lt_gt_contravar x PI H0); intro H6; + change (- PI < - x) in H6; generalize (Rplus_lt_compat_l PI (- PI) (- x) H6). + rewrite Rplus_opp_r. + replace (PI + - x) with (PI - x). + intro H7; + elim + (SIN (PI - x) (Rlt_le 0 (PI - x) H7) + (Rlt_le (PI - x) PI (Rlt_trans (PI - x) (PI / 2) PI H5 PI2_Rlt_PI))); + intros H8 _; + generalize (sin_lb_gt_0 (PI - x) H7 (Rlt_le (PI - x) (PI / 2) H5)); + intro H9; apply (Rlt_le_trans 0 (sin_lb (PI - x)) (sin (PI - x)) H9 H8). + reflexivity. + pattern PI at 2 in |- *; rewrite double_var; ring. + reflexivity. +Qed. + +Theorem cos_gt_0 : forall x:R, - (PI / 2) < x -> x < PI / 2 -> 0 < cos x. +Proof. + intros; rewrite cos_sin; + generalize (Rplus_lt_compat_l (PI / 2) (- (PI / 2)) x H). + rewrite Rplus_opp_r; intro H1; + generalize (Rplus_lt_compat_l (PI / 2) x (PI / 2) H0); + rewrite <- double_var; intro H2; apply (sin_gt_0 (PI / 2 + x) H1 H2). +Qed. + +Lemma sin_ge_0 : forall x:R, 0 <= x -> x <= PI -> 0 <= sin x. +Proof. + intros x H1 H2; elim H1; intro H3; + [ elim H2; intro H4; + [ left; apply (sin_gt_0 x H3 H4) + | rewrite H4; right; symmetry in |- *; apply sin_PI ] + | rewrite <- H3; right; symmetry in |- *; apply sin_0 ]. +Qed. + +Lemma cos_ge_0 : forall x:R, - (PI / 2) <= x -> x <= PI / 2 -> 0 <= cos x. +Proof. + intros x H1 H2; elim H1; intro H3; + [ elim H2; intro H4; + [ left; apply (cos_gt_0 x H3 H4) + | rewrite H4; right; symmetry in |- *; apply cos_PI2 ] + | rewrite <- H3; rewrite cos_neg; right; symmetry in |- *; apply cos_PI2 ]. +Qed. + +Lemma sin_le_0 : forall x:R, PI <= x -> x <= 2 * PI -> sin x <= 0. +Proof. + intros x H1 H2; apply Rge_le; rewrite <- Ropp_0; + rewrite <- (Ropp_involutive (sin x)); apply Ropp_le_ge_contravar; + rewrite <- neg_sin; replace (x + PI) with (x - PI + 2 * INR 1 * PI); + [ rewrite (sin_period (x - PI) 1); apply sin_ge_0; + [ replace (x - PI) with (x + - PI); + [ rewrite Rplus_comm; replace 0 with (- PI + PI); + [ apply Rplus_le_compat_l; assumption | ring ] + | ring ] + | replace (x - PI) with (x + - PI); rewrite Rplus_comm; + [ pattern PI at 2 in |- *; replace PI with (- PI + 2 * PI); + [ apply Rplus_le_compat_l; assumption | ring ] + | ring ] ] + | unfold INR in |- *; ring ]. +Qed. + +Lemma cos_le_0 : forall x:R, PI / 2 <= x -> x <= 3 * (PI / 2) -> cos x <= 0. +Proof. + intros x H1 H2; apply Rge_le; rewrite <- Ropp_0; + rewrite <- (Ropp_involutive (cos x)); apply Ropp_le_ge_contravar; + rewrite <- neg_cos; replace (x + PI) with (x - PI + 2 * INR 1 * PI). + rewrite cos_period; apply cos_ge_0. + replace (- (PI / 2)) with (- PI + PI / 2). + unfold Rminus in |- *; rewrite (Rplus_comm x); apply Rplus_le_compat_l; + assumption. + pattern PI at 1 in |- *; rewrite (double_var PI); rewrite Ropp_plus_distr; + ring. + unfold Rminus in |- *; rewrite Rplus_comm; + replace (PI / 2) with (- PI + 3 * (PI / 2)). + apply Rplus_le_compat_l; assumption. + pattern PI at 1 in |- *; rewrite (double_var PI); rewrite Ropp_plus_distr; + ring. + unfold INR in |- *; ring. +Qed. + +Lemma sin_lt_0 : forall x:R, PI < x -> x < 2 * PI -> sin x < 0. +Proof. + intros x H1 H2; rewrite <- Ropp_0; rewrite <- (Ropp_involutive (sin x)); + apply Ropp_lt_gt_contravar; rewrite <- neg_sin; + replace (x + PI) with (x - PI + 2 * INR 1 * PI); + [ rewrite (sin_period (x - PI) 1); apply sin_gt_0; + [ replace (x - PI) with (x + - PI); + [ rewrite Rplus_comm; replace 0 with (- PI + PI); + [ apply Rplus_lt_compat_l; assumption | ring ] + | ring ] + | replace (x - PI) with (x + - PI); rewrite Rplus_comm; + [ pattern PI at 2 in |- *; replace PI with (- PI + 2 * PI); + [ apply Rplus_lt_compat_l; assumption | ring ] + | ring ] ] + | unfold INR in |- *; ring ]. +Qed. + +Lemma sin_lt_0_var : forall x:R, - PI < x -> x < 0 -> sin x < 0. +Proof. + intros; generalize (Rplus_lt_compat_l (2 * PI) (- PI) x H); + replace (2 * PI + - PI) with PI; + [ intro H1; rewrite Rplus_comm in H1; + generalize (Rplus_lt_compat_l (2 * PI) x 0 H0); + intro H2; rewrite (Rplus_comm (2 * PI)) in H2; + rewrite <- (Rplus_comm 0) in H2; rewrite Rplus_0_l in H2; + rewrite <- (sin_period x 1); unfold INR in |- *; + replace (2 * 1 * PI) with (2 * PI); + [ apply (sin_lt_0 (x + 2 * PI) H1 H2) | ring ] + | ring ]. +Qed. + +Lemma cos_lt_0 : forall x:R, PI / 2 < x -> x < 3 * (PI / 2) -> cos x < 0. +Proof. + intros x H1 H2; rewrite <- Ropp_0; rewrite <- (Ropp_involutive (cos x)); + apply Ropp_lt_gt_contravar; rewrite <- neg_cos; + replace (x + PI) with (x - PI + 2 * INR 1 * PI). + rewrite cos_period; apply cos_gt_0. + replace (- (PI / 2)) with (- PI + PI / 2). + unfold Rminus in |- *; rewrite (Rplus_comm x); apply Rplus_lt_compat_l; + assumption. + pattern PI at 1 in |- *; rewrite (double_var PI); rewrite Ropp_plus_distr; + ring. + unfold Rminus in |- *; rewrite Rplus_comm; + replace (PI / 2) with (- PI + 3 * (PI / 2)). + apply Rplus_lt_compat_l; assumption. + pattern PI at 1 in |- *; rewrite (double_var PI); rewrite Ropp_plus_distr; + ring. + unfold INR in |- *; ring. +Qed. + +Lemma tan_gt_0 : forall x:R, 0 < x -> x < PI / 2 -> 0 < tan x. +Proof. + intros x H1 H2; unfold tan in |- *; generalize _PI2_RLT_0; + generalize (Rlt_trans 0 x (PI / 2) H1 H2); intros; + generalize (Rlt_trans (- (PI / 2)) 0 x H0 H1); intro H5; + generalize (Rlt_trans x (PI / 2) PI H2 PI2_Rlt_PI); + intro H7; unfold Rdiv in |- *; apply Rmult_lt_0_compat. + apply sin_gt_0; assumption. + apply Rinv_0_lt_compat; apply cos_gt_0; assumption. +Qed. + +Lemma tan_lt_0 : forall x:R, - (PI / 2) < x -> x < 0 -> tan x < 0. +Proof. + intros x H1 H2; unfold tan in |- *; + generalize (cos_gt_0 x H1 (Rlt_trans x 0 (PI / 2) H2 PI2_RGT_0)); + intro H3; rewrite <- Ropp_0; + replace (sin x / cos x) with (- (- sin x / cos x)). + rewrite <- sin_neg; apply Ropp_gt_lt_contravar; + change (0 < sin (- x) / cos x) in |- *; unfold Rdiv in |- *; + apply Rmult_lt_0_compat. + apply sin_gt_0. + rewrite <- Ropp_0; apply Ropp_gt_lt_contravar; assumption. + apply Rlt_trans with (PI / 2). + rewrite <- (Ropp_involutive (PI / 2)); apply Ropp_gt_lt_contravar; assumption. + apply PI2_Rlt_PI. + apply Rinv_0_lt_compat; assumption. + unfold Rdiv in |- *; ring. +Qed. + +Lemma cos_ge_0_3PI2 : + forall x:R, 3 * (PI / 2) <= x -> x <= 2 * PI -> 0 <= cos x. +Proof. + intros; rewrite <- cos_neg; rewrite <- (cos_period (- x) 1); + unfold INR in |- *; replace (- x + 2 * 1 * PI) with (2 * PI - x). + generalize (Ropp_le_ge_contravar x (2 * PI) H0); intro H1; + generalize (Rge_le (- x) (- (2 * PI)) H1); clear H1; + intro H1; generalize (Rplus_le_compat_l (2 * PI) (- (2 * PI)) (- x) H1). + rewrite Rplus_opp_r. + intro H2; generalize (Ropp_le_ge_contravar (3 * (PI / 2)) x H); intro H3; + generalize (Rge_le (- (3 * (PI / 2))) (- x) H3); clear H3; + intro H3; + generalize (Rplus_le_compat_l (2 * PI) (- x) (- (3 * (PI / 2))) H3). + replace (2 * PI + - (3 * (PI / 2))) with (PI / 2). + intro H4; + apply + (cos_ge_0 (2 * PI - x) + (Rlt_le (- (PI / 2)) (2 * PI - x) + (Rlt_le_trans (- (PI / 2)) 0 (2 * PI - x) _PI2_RLT_0 H2)) H4). + rewrite double; pattern PI at 2 3 in |- *; rewrite double_var; ring. + ring. +Qed. + +Lemma form1 : + forall p q:R, cos p + cos q = 2 * cos ((p - q) / 2) * cos ((p + q) / 2). +Proof. + intros p q; pattern p at 1 in |- *; + replace p with ((p - q) / 2 + (p + q) / 2). + rewrite <- (cos_neg q); replace (- q) with ((p - q) / 2 - (p + q) / 2). + rewrite cos_plus; rewrite cos_minus; ring. + pattern q at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. + pattern p at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. +Qed. + +Lemma form2 : + forall p q:R, cos p - cos q = -2 * sin ((p - q) / 2) * sin ((p + q) / 2). +Proof. + intros p q; pattern p at 1 in |- *; + replace p with ((p - q) / 2 + (p + q) / 2). + rewrite <- (cos_neg q); replace (- q) with ((p - q) / 2 - (p + q) / 2). + rewrite cos_plus; rewrite cos_minus; ring. + pattern q at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. + pattern p at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. +Qed. + +Lemma form3 : + forall p q:R, sin p + sin q = 2 * cos ((p - q) / 2) * sin ((p + q) / 2). +Proof. + intros p q; pattern p at 1 in |- *; + replace p with ((p - q) / 2 + (p + q) / 2). + pattern q at 3 in |- *; replace q with ((p + q) / 2 - (p - q) / 2). + rewrite sin_plus; rewrite sin_minus; ring. + pattern q at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. + pattern p at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. +Qed. + +Lemma form4 : + forall p q:R, sin p - sin q = 2 * cos ((p + q) / 2) * sin ((p - q) / 2). +Proof. + intros p q; pattern p at 1 in |- *; + replace p with ((p - q) / 2 + (p + q) / 2). + pattern q at 3 in |- *; replace q with ((p + q) / 2 - (p - q) / 2). + rewrite sin_plus; rewrite sin_minus; ring. + pattern q at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. + pattern p at 3 in |- *; rewrite double_var; unfold Rdiv in |- *; ring. + +Qed. + +Lemma sin_increasing_0 : + forall x y:R, + - (PI / 2) <= x -> + x <= PI / 2 -> - (PI / 2) <= y -> y <= PI / 2 -> sin x < sin y -> x < y. +Proof. + intros; cut (sin ((x - y) / 2) < 0). + intro H4; case (Rtotal_order ((x - y) / 2) 0); intro H5. + assert (Hyp : 0 < 2). + prove_sup0. + generalize (Rmult_lt_compat_l 2 ((x - y) / 2) 0 Hyp H5). + unfold Rdiv in |- *. + rewrite <- Rmult_assoc. + rewrite Rinv_r_simpl_m. + rewrite Rmult_0_r. + clear H5; intro H5; apply Rminus_lt; assumption. + discrR. + elim H5; intro H6. + rewrite H6 in H4; rewrite sin_0 in H4; elim (Rlt_irrefl 0 H4). + change (0 < (x - y) / 2) in H6; + generalize (Ropp_le_ge_contravar (- (PI / 2)) y H1). + rewrite Ropp_involutive. + intro H7; generalize (Rge_le (PI / 2) (- y) H7); clear H7; intro H7; + generalize (Rplus_le_compat x (PI / 2) (- y) (PI / 2) H0 H7). + rewrite <- double_var. + intro H8. + assert (Hyp : 0 < 2). + prove_sup0. + generalize + (Rmult_le_compat_l (/ 2) (x - y) PI + (Rlt_le 0 (/ 2) (Rinv_0_lt_compat 2 Hyp)) H8). + repeat rewrite (Rmult_comm (/ 2)). + intro H9; + generalize + (sin_gt_0 ((x - y) / 2) H6 + (Rle_lt_trans ((x - y) / 2) (PI / 2) PI H9 PI2_Rlt_PI)); + intro H10; + elim + (Rlt_irrefl (sin ((x - y) / 2)) + (Rlt_trans (sin ((x - y) / 2)) 0 (sin ((x - y) / 2)) H4 H10)). + generalize (Rlt_minus (sin x) (sin y) H3); clear H3; intro H3; + rewrite form4 in H3; + generalize (Rplus_le_compat x (PI / 2) y (PI / 2) H0 H2). + rewrite <- double_var. + assert (Hyp : 0 < 2). + prove_sup0. + intro H4; + generalize + (Rmult_le_compat_l (/ 2) (x + y) PI + (Rlt_le 0 (/ 2) (Rinv_0_lt_compat 2 Hyp)) H4). + repeat rewrite (Rmult_comm (/ 2)). + clear H4; intro H4; + generalize (Rplus_le_compat (- (PI / 2)) x (- (PI / 2)) y H H1); + replace (- (PI / 2) + - (PI / 2)) with (- PI). + intro H5; + generalize + (Rmult_le_compat_l (/ 2) (- PI) (x + y) + (Rlt_le 0 (/ 2) (Rinv_0_lt_compat 2 Hyp)) H5). + replace (/ 2 * (x + y)) with ((x + y) / 2). + replace (/ 2 * - PI) with (- (PI / 2)). + clear H5; intro H5; elim H4; intro H40. + elim H5; intro H50. + generalize (cos_gt_0 ((x + y) / 2) H50 H40); intro H6; + generalize (Rmult_lt_compat_l 2 0 (cos ((x + y) / 2)) Hyp H6). + rewrite Rmult_0_r. + clear H6; intro H6; case (Rcase_abs (sin ((x - y) / 2))); intro H7. + assumption. + generalize (Rge_le (sin ((x - y) / 2)) 0 H7); clear H7; intro H7; + generalize + (Rmult_le_pos (2 * cos ((x + y) / 2)) (sin ((x - y) / 2)) + (Rlt_le 0 (2 * cos ((x + y) / 2)) H6) H7); intro H8; + generalize + (Rle_lt_trans 0 (2 * cos ((x + y) / 2) * sin ((x - y) / 2)) 0 H8 H3); + intro H9; elim (Rlt_irrefl 0 H9). + rewrite <- H50 in H3; rewrite cos_neg in H3; rewrite cos_PI2 in H3; + rewrite Rmult_0_r in H3; rewrite Rmult_0_l in H3; + elim (Rlt_irrefl 0 H3). + unfold Rdiv in H3. + rewrite H40 in H3; assert (H50 := cos_PI2); unfold Rdiv in H50; + rewrite H50 in H3; rewrite Rmult_0_r in H3; rewrite Rmult_0_l in H3; + elim (Rlt_irrefl 0 H3). + unfold Rdiv in |- *. + rewrite <- Ropp_mult_distr_l_reverse. + apply Rmult_comm. + unfold Rdiv in |- *; apply Rmult_comm. + pattern PI at 1 in |- *; rewrite double_var. + rewrite Ropp_plus_distr. + reflexivity. +Qed. + +Lemma sin_increasing_1 : + forall x y:R, + - (PI / 2) <= x -> + x <= PI / 2 -> - (PI / 2) <= y -> y <= PI / 2 -> x < y -> sin x < sin y. +Proof. + intros; generalize (Rplus_lt_compat_l x x y H3); intro H4; + generalize (Rplus_le_compat (- (PI / 2)) x (- (PI / 2)) x H H); + replace (- (PI / 2) + - (PI / 2)) with (- PI). + assert (Hyp : 0 < 2). + prove_sup0. + intro H5; generalize (Rle_lt_trans (- PI) (x + x) (x + y) H5 H4); intro H6; + generalize + (Rmult_lt_compat_l (/ 2) (- PI) (x + y) (Rinv_0_lt_compat 2 Hyp) H6); + replace (/ 2 * - PI) with (- (PI / 2)). + replace (/ 2 * (x + y)) with ((x + y) / 2). + clear H4 H5 H6; intro H4; generalize (Rplus_lt_compat_l y x y H3); intro H5; + rewrite Rplus_comm in H5; + generalize (Rplus_le_compat y (PI / 2) y (PI / 2) H2 H2). + rewrite <- double_var. + intro H6; generalize (Rlt_le_trans (x + y) (y + y) PI H5 H6); intro H7; + generalize (Rmult_lt_compat_l (/ 2) (x + y) PI (Rinv_0_lt_compat 2 Hyp) H7); + replace (/ 2 * PI) with (PI / 2). + replace (/ 2 * (x + y)) with ((x + y) / 2). + clear H5 H6 H7; intro H5; generalize (Ropp_le_ge_contravar (- (PI / 2)) y H1); + rewrite Ropp_involutive; clear H1; intro H1; + generalize (Rge_le (PI / 2) (- y) H1); clear H1; intro H1; + generalize (Ropp_le_ge_contravar y (PI / 2) H2); clear H2; + intro H2; generalize (Rge_le (- y) (- (PI / 2)) H2); + clear H2; intro H2; generalize (Rplus_lt_compat_l (- y) x y H3); + replace (- y + x) with (x - y). + rewrite Rplus_opp_l. + intro H6; + generalize (Rmult_lt_compat_l (/ 2) (x - y) 0 (Rinv_0_lt_compat 2 Hyp) H6); + rewrite Rmult_0_r; replace (/ 2 * (x - y)) with ((x - y) / 2). + clear H6; intro H6; + generalize (Rplus_le_compat (- (PI / 2)) x (- (PI / 2)) (- y) H H2); + replace (- (PI / 2) + - (PI / 2)) with (- PI). + replace (x + - y) with (x - y). + intro H7; + generalize + (Rmult_le_compat_l (/ 2) (- PI) (x - y) + (Rlt_le 0 (/ 2) (Rinv_0_lt_compat 2 Hyp)) H7); + replace (/ 2 * - PI) with (- (PI / 2)). + replace (/ 2 * (x - y)) with ((x - y) / 2). + clear H7; intro H7; clear H H0 H1 H2; apply Rminus_lt; rewrite form4; + generalize (cos_gt_0 ((x + y) / 2) H4 H5); intro H8; + generalize (Rmult_lt_0_compat 2 (cos ((x + y) / 2)) Hyp H8); + clear H8; intro H8; cut (- PI < - (PI / 2)). + intro H9; + generalize + (sin_lt_0_var ((x - y) / 2) + (Rlt_le_trans (- PI) (- (PI / 2)) ((x - y) / 2) H9 H7) H6); + intro H10; + generalize + (Rmult_lt_gt_compat_neg_l (sin ((x - y) / 2)) 0 ( + 2 * cos ((x + y) / 2)) H10 H8); intro H11; rewrite Rmult_0_r in H11; + rewrite Rmult_comm; assumption. + apply Ropp_lt_gt_contravar; apply PI2_Rlt_PI. + unfold Rdiv in |- *; apply Rmult_comm. + unfold Rdiv in |- *; rewrite <- Ropp_mult_distr_l_reverse; apply Rmult_comm. + reflexivity. + pattern PI at 1 in |- *; rewrite double_var. + rewrite Ropp_plus_distr. + reflexivity. + unfold Rdiv in |- *; apply Rmult_comm. + unfold Rminus in |- *; apply Rplus_comm. + unfold Rdiv in |- *; apply Rmult_comm. + unfold Rdiv in |- *; apply Rmult_comm. + unfold Rdiv in |- *; apply Rmult_comm. + unfold Rdiv in |- *. + rewrite <- Ropp_mult_distr_l_reverse. + apply Rmult_comm. + pattern PI at 1 in |- *; rewrite double_var. + rewrite Ropp_plus_distr. + reflexivity. +Qed. + +Lemma sin_decreasing_0 : + forall x y:R, + x <= 3 * (PI / 2) -> + PI / 2 <= x -> y <= 3 * (PI / 2) -> PI / 2 <= y -> sin x < sin y -> y < x. +Proof. + intros; rewrite <- (sin_PI_x x) in H3; rewrite <- (sin_PI_x y) in H3; + generalize (Ropp_lt_gt_contravar (sin (PI - x)) (sin (PI - y)) H3); + repeat rewrite <- sin_neg; + generalize (Rplus_le_compat_l (- PI) x (3 * (PI / 2)) H); + generalize (Rplus_le_compat_l (- PI) (PI / 2) x H0); + generalize (Rplus_le_compat_l (- PI) y (3 * (PI / 2)) H1); + generalize (Rplus_le_compat_l (- PI) (PI / 2) y H2); + replace (- PI + x) with (x - PI). + replace (- PI + PI / 2) with (- (PI / 2)). + replace (- PI + y) with (y - PI). + replace (- PI + 3 * (PI / 2)) with (PI / 2). + replace (- (PI - x)) with (x - PI). + replace (- (PI - y)) with (y - PI). + intros; change (sin (y - PI) < sin (x - PI)) in H8; + apply Rplus_lt_reg_r with (- PI); rewrite Rplus_comm; + replace (y + - PI) with (y - PI). + rewrite Rplus_comm; replace (x + - PI) with (x - PI). + apply (sin_increasing_0 (y - PI) (x - PI) H4 H5 H6 H7 H8). + reflexivity. + reflexivity. + unfold Rminus in |- *; rewrite Ropp_plus_distr. + rewrite Ropp_involutive. + apply Rplus_comm. + unfold Rminus in |- *; rewrite Ropp_plus_distr. + rewrite Ropp_involutive. + apply Rplus_comm. + pattern PI at 2 in |- *; rewrite double_var. + rewrite Ropp_plus_distr. + ring. + unfold Rminus in |- *; apply Rplus_comm. + pattern PI at 2 in |- *; rewrite double_var. + rewrite Ropp_plus_distr. + ring. + unfold Rminus in |- *; apply Rplus_comm. +Qed. + +Lemma sin_decreasing_1 : + forall x y:R, + x <= 3 * (PI / 2) -> + PI / 2 <= x -> y <= 3 * (PI / 2) -> PI / 2 <= y -> x < y -> sin y < sin x. +Proof. + intros; rewrite <- (sin_PI_x x); rewrite <- (sin_PI_x y); + generalize (Rplus_le_compat_l (- PI) x (3 * (PI / 2)) H); + generalize (Rplus_le_compat_l (- PI) (PI / 2) x H0); + generalize (Rplus_le_compat_l (- PI) y (3 * (PI / 2)) H1); + generalize (Rplus_le_compat_l (- PI) (PI / 2) y H2); + generalize (Rplus_lt_compat_l (- PI) x y H3); + replace (- PI + PI / 2) with (- (PI / 2)). + replace (- PI + y) with (y - PI). + replace (- PI + 3 * (PI / 2)) with (PI / 2). + replace (- PI + x) with (x - PI). + intros; apply Ropp_lt_cancel; repeat rewrite <- sin_neg; + replace (- (PI - x)) with (x - PI). + replace (- (PI - y)) with (y - PI). + apply (sin_increasing_1 (x - PI) (y - PI) H7 H8 H5 H6 H4). + unfold Rminus in |- *; rewrite Ropp_plus_distr. + rewrite Ropp_involutive. + apply Rplus_comm. + unfold Rminus in |- *; rewrite Ropp_plus_distr. + rewrite Ropp_involutive. + apply Rplus_comm. + unfold Rminus in |- *; apply Rplus_comm. + pattern PI at 2 in |- *; rewrite double_var; ring. + unfold Rminus in |- *; apply Rplus_comm. + pattern PI at 2 in |- *; rewrite double_var; ring. +Qed. + +Lemma cos_increasing_0 : + forall x y:R, + PI <= x -> x <= 2 * PI -> PI <= y -> y <= 2 * PI -> cos x < cos y -> x < y. +Proof. + intros x y H1 H2 H3 H4; rewrite <- (cos_neg x); rewrite <- (cos_neg y); + rewrite <- (cos_period (- x) 1); rewrite <- (cos_period (- y) 1); + unfold INR in |- *; + replace (- x + 2 * 1 * PI) with (PI / 2 - (x - 3 * (PI / 2))). + replace (- y + 2 * 1 * PI) with (PI / 2 - (y - 3 * (PI / 2))). + repeat rewrite cos_shift; intro H5; + generalize (Rplus_le_compat_l (-3 * (PI / 2)) PI x H1); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) x (2 * PI) H2); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) PI y H3); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) y (2 * PI) H4). + replace (-3 * (PI / 2) + y) with (y - 3 * (PI / 2)). + replace (-3 * (PI / 2) + x) with (x - 3 * (PI / 2)). + replace (-3 * (PI / 2) + 2 * PI) with (PI / 2). + replace (-3 * (PI / 2) + PI) with (- (PI / 2)). + clear H1 H2 H3 H4; intros H1 H2 H3 H4; + apply Rplus_lt_reg_r with (-3 * (PI / 2)); + replace (-3 * (PI / 2) + x) with (x - 3 * (PI / 2)). + replace (-3 * (PI / 2) + y) with (y - 3 * (PI / 2)). + apply (sin_increasing_0 (x - 3 * (PI / 2)) (y - 3 * (PI / 2)) H4 H3 H2 H1 H5). + unfold Rminus in |- *. + rewrite Ropp_mult_distr_l_reverse. + apply Rplus_comm. + unfold Rminus in |- *. + rewrite Ropp_mult_distr_l_reverse. + apply Rplus_comm. + pattern PI at 3 in |- *; rewrite double_var. + ring. + rewrite double; pattern PI at 3 4 in |- *; rewrite double_var. + ring. + unfold Rminus in |- *. + rewrite Ropp_mult_distr_l_reverse. + apply Rplus_comm. + unfold Rminus in |- *. + rewrite Ropp_mult_distr_l_reverse. + apply Rplus_comm. + rewrite Rmult_1_r. + rewrite (double PI); pattern PI at 3 4 in |- *; rewrite double_var. + ring. + rewrite Rmult_1_r. + rewrite (double PI); pattern PI at 3 4 in |- *; rewrite double_var. + ring. +Qed. + +Lemma cos_increasing_1 : + forall x y:R, + PI <= x -> x <= 2 * PI -> PI <= y -> y <= 2 * PI -> x < y -> cos x < cos y. +Proof. + intros x y H1 H2 H3 H4 H5; + generalize (Rplus_le_compat_l (-3 * (PI / 2)) PI x H1); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) x (2 * PI) H2); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) PI y H3); + generalize (Rplus_le_compat_l (-3 * (PI / 2)) y (2 * PI) H4); + generalize (Rplus_lt_compat_l (-3 * (PI / 2)) x y H5); + rewrite <- (cos_neg x); rewrite <- (cos_neg y); + rewrite <- (cos_period (- x) 1); rewrite <- (cos_period (- y) 1); + unfold INR in |- *; replace (-3 * (PI / 2) + x) with (x - 3 * (PI / 2)). + replace (-3 * (PI / 2) + y) with (y - 3 * (PI / 2)). + replace (-3 * (PI / 2) + PI) with (- (PI / 2)). + replace (-3 * (PI / 2) + 2 * PI) with (PI / 2). + clear H1 H2 H3 H4 H5; intros H1 H2 H3 H4 H5; + replace (- x + 2 * 1 * PI) with (PI / 2 - (x - 3 * (PI / 2))). + replace (- y + 2 * 1 * PI) with (PI / 2 - (y - 3 * (PI / 2))). + repeat rewrite cos_shift; + apply + (sin_increasing_1 (x - 3 * (PI / 2)) (y - 3 * (PI / 2)) H5 H4 H3 H2 H1). + rewrite Rmult_1_r. + rewrite (double PI); pattern PI at 3 4 in |- *; rewrite double_var. + ring. + rewrite Rmult_1_r. + rewrite (double PI); pattern PI at 3 4 in |- *; rewrite double_var. + ring. + rewrite (double PI); pattern PI at 3 4 in |- *; rewrite double_var. + ring. + pattern PI at 3 in |- *; rewrite double_var; ring. + unfold Rminus in |- *. + rewrite <- Ropp_mult_distr_l_reverse. + apply Rplus_comm. + unfold Rminus in |- *. + rewrite <- Ropp_mult_distr_l_reverse. + apply Rplus_comm. +Qed. + +Lemma cos_decreasing_0 : + forall x y:R, + 0 <= x -> x <= PI -> 0 <= y -> y <= PI -> cos x < cos y -> y < x. +Proof. + intros; generalize (Ropp_lt_gt_contravar (cos x) (cos y) H3); + repeat rewrite <- neg_cos; intro H4; + change (cos (y + PI) < cos (x + PI)) in H4; rewrite (Rplus_comm x) in H4; + rewrite (Rplus_comm y) in H4; generalize (Rplus_le_compat_l PI 0 x H); + generalize (Rplus_le_compat_l PI x PI H0); + generalize (Rplus_le_compat_l PI 0 y H1); + generalize (Rplus_le_compat_l PI y PI H2); rewrite Rplus_0_r. + rewrite <- double. + clear H H0 H1 H2 H3; intros; apply Rplus_lt_reg_r with PI; + apply (cos_increasing_0 (PI + y) (PI + x) H0 H H2 H1 H4). +Qed. + +Lemma cos_decreasing_1 : + forall x y:R, + 0 <= x -> x <= PI -> 0 <= y -> y <= PI -> x < y -> cos y < cos x. +Proof. + intros; apply Ropp_lt_cancel; repeat rewrite <- neg_cos; + rewrite (Rplus_comm x); rewrite (Rplus_comm y); + generalize (Rplus_le_compat_l PI 0 x H); + generalize (Rplus_le_compat_l PI x PI H0); + generalize (Rplus_le_compat_l PI 0 y H1); + generalize (Rplus_le_compat_l PI y PI H2); rewrite Rplus_0_r. + rewrite <- double. + generalize (Rplus_lt_compat_l PI x y H3); clear H H0 H1 H2 H3; intros; + apply (cos_increasing_1 (PI + x) (PI + y) H3 H2 H1 H0 H). +Qed. + +Lemma tan_diff : + forall x y:R, + cos x <> 0 -> cos y <> 0 -> tan x - tan y = sin (x - y) / (cos x * cos y). +Proof. + intros; unfold tan in |- *; rewrite sin_minus. + unfold Rdiv in |- *. + unfold Rminus in |- *. + rewrite Rmult_plus_distr_r. + rewrite Rinv_mult_distr. + repeat rewrite (Rmult_comm (sin x)). + repeat rewrite Rmult_assoc. + rewrite (Rmult_comm (cos y)). + repeat rewrite Rmult_assoc. + rewrite <- Rinv_l_sym. + rewrite Rmult_1_r. + rewrite (Rmult_comm (sin x)). + apply Rplus_eq_compat_l. + rewrite <- Ropp_mult_distr_l_reverse. + rewrite <- Ropp_mult_distr_r_reverse. + rewrite (Rmult_comm (/ cos x)). + repeat rewrite Rmult_assoc. + rewrite (Rmult_comm (cos x)). + repeat rewrite Rmult_assoc. + rewrite <- Rinv_l_sym. + rewrite Rmult_1_r. + reflexivity. + assumption. + assumption. + assumption. + assumption. +Qed. + +Lemma tan_increasing_0 : + forall x y:R, + - (PI / 4) <= x -> + x <= PI / 4 -> - (PI / 4) <= y -> y <= PI / 4 -> tan x < tan y -> x < y. +Proof. + intros; generalize PI4_RLT_PI2; intro H4; + generalize (Ropp_lt_gt_contravar (PI / 4) (PI / 2) H4); + intro H5; change (- (PI / 2) < - (PI / 4)) in H5; + generalize + (cos_gt_0 x (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) x H5 H) + (Rle_lt_trans x (PI / 4) (PI / 2) H0 H4)); intro HP1; + generalize + (cos_gt_0 y (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) y H5 H1) + (Rle_lt_trans y (PI / 4) (PI / 2) H2 H4)); intro HP2; + generalize + (not_eq_sym + (Rlt_not_eq 0 (cos x) + (cos_gt_0 x (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) x H5 H) + (Rle_lt_trans x (PI / 4) (PI / 2) H0 H4)))); + intro H6; + generalize + (not_eq_sym + (Rlt_not_eq 0 (cos y) + (cos_gt_0 y (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) y H5 H1) + (Rle_lt_trans y (PI / 4) (PI / 2) H2 H4)))); + intro H7; generalize (tan_diff x y H6 H7); intro H8; + generalize (Rlt_minus (tan x) (tan y) H3); clear H3; + intro H3; rewrite H8 in H3; cut (sin (x - y) < 0). + intro H9; generalize (Ropp_le_ge_contravar (- (PI / 4)) y H1); + rewrite Ropp_involutive; intro H10; generalize (Rge_le (PI / 4) (- y) H10); + clear H10; intro H10; generalize (Ropp_le_ge_contravar y (PI / 4) H2); + intro H11; generalize (Rge_le (- y) (- (PI / 4)) H11); + clear H11; intro H11; + generalize (Rplus_le_compat (- (PI / 4)) x (- (PI / 4)) (- y) H H11); + generalize (Rplus_le_compat x (PI / 4) (- y) (PI / 4) H0 H10); + replace (x + - y) with (x - y). + replace (PI / 4 + PI / 4) with (PI / 2). + replace (- (PI / 4) + - (PI / 4)) with (- (PI / 2)). + intros; case (Rtotal_order 0 (x - y)); intro H14. + generalize + (sin_gt_0 (x - y) H14 (Rle_lt_trans (x - y) (PI / 2) PI H12 PI2_Rlt_PI)); + intro H15; elim (Rlt_irrefl 0 (Rlt_trans 0 (sin (x - y)) 0 H15 H9)). + elim H14; intro H15. + rewrite <- H15 in H9; rewrite sin_0 in H9; elim (Rlt_irrefl 0 H9). + apply Rminus_lt; assumption. + pattern PI at 1 in |- *; rewrite double_var. + unfold Rdiv in |- *. + rewrite Rmult_plus_distr_r. + repeat rewrite Rmult_assoc. + rewrite <- Rinv_mult_distr. + rewrite Ropp_plus_distr. + replace 4 with 4. + reflexivity. + ring. + discrR. + discrR. + pattern PI at 1 in |- *; rewrite double_var. + unfold Rdiv in |- *. + rewrite Rmult_plus_distr_r. + repeat rewrite Rmult_assoc. + rewrite <- Rinv_mult_distr. + replace 4 with 4. + reflexivity. + ring. + discrR. + discrR. + reflexivity. + case (Rcase_abs (sin (x - y))); intro H9. + assumption. + generalize (Rge_le (sin (x - y)) 0 H9); clear H9; intro H9; + generalize (Rinv_0_lt_compat (cos x) HP1); intro H10; + generalize (Rinv_0_lt_compat (cos y) HP2); intro H11; + generalize (Rmult_lt_0_compat (/ cos x) (/ cos y) H10 H11); + replace (/ cos x * / cos y) with (/ (cos x * cos y)). + intro H12; + generalize + (Rmult_le_pos (sin (x - y)) (/ (cos x * cos y)) H9 + (Rlt_le 0 (/ (cos x * cos y)) H12)); intro H13; + elim + (Rlt_irrefl 0 (Rle_lt_trans 0 (sin (x - y) * / (cos x * cos y)) 0 H13 H3)). + rewrite Rinv_mult_distr. + reflexivity. + assumption. + assumption. +Qed. + +Lemma tan_increasing_1 : + forall x y:R, + - (PI / 4) <= x -> + x <= PI / 4 -> - (PI / 4) <= y -> y <= PI / 4 -> x < y -> tan x < tan y. +Proof. + intros; apply Rminus_lt; generalize PI4_RLT_PI2; intro H4; + generalize (Ropp_lt_gt_contravar (PI / 4) (PI / 2) H4); + intro H5; change (- (PI / 2) < - (PI / 4)) in H5; + generalize + (cos_gt_0 x (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) x H5 H) + (Rle_lt_trans x (PI / 4) (PI / 2) H0 H4)); intro HP1; + generalize + (cos_gt_0 y (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) y H5 H1) + (Rle_lt_trans y (PI / 4) (PI / 2) H2 H4)); intro HP2; + generalize + (not_eq_sym + (Rlt_not_eq 0 (cos x) + (cos_gt_0 x (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) x H5 H) + (Rle_lt_trans x (PI / 4) (PI / 2) H0 H4)))); + intro H6; + generalize + (not_eq_sym + (Rlt_not_eq 0 (cos y) + (cos_gt_0 y (Rlt_le_trans (- (PI / 2)) (- (PI / 4)) y H5 H1) + (Rle_lt_trans y (PI / 4) (PI / 2) H2 H4)))); + intro H7; rewrite (tan_diff x y H6 H7); + generalize (Rinv_0_lt_compat (cos x) HP1); intro H10; + generalize (Rinv_0_lt_compat (cos y) HP2); intro H11; + generalize (Rmult_lt_0_compat (/ cos x) (/ cos y) H10 H11); + replace (/ cos x * / cos y) with (/ (cos x * cos y)). + clear H10 H11; intro H8; generalize (Ropp_le_ge_contravar y (PI / 4) H2); + intro H11; generalize (Rge_le (- y) (- (PI / 4)) H11); + clear H11; intro H11; + generalize (Rplus_le_compat (- (PI / 4)) x (- (PI / 4)) (- y) H H11); + replace (x + - y) with (x - y). + replace (- (PI / 4) + - (PI / 4)) with (- (PI / 2)). + clear H11; intro H9; generalize (Rlt_minus x y H3); clear H3; intro H3; + clear H H0 H1 H2 H4 H5 HP1 HP2; generalize PI2_Rlt_PI; + intro H1; generalize (Ropp_lt_gt_contravar (PI / 2) PI H1); + clear H1; intro H1; + generalize + (sin_lt_0_var (x - y) (Rlt_le_trans (- PI) (- (PI / 2)) (x - y) H1 H9) H3); + intro H2; + generalize + (Rmult_lt_gt_compat_neg_l (sin (x - y)) 0 (/ (cos x * cos y)) H2 H8); + rewrite Rmult_0_r; intro H4; assumption. + pattern PI at 1 in |- *; rewrite double_var. + unfold Rdiv in |- *. + rewrite Rmult_plus_distr_r. + repeat rewrite Rmult_assoc. + rewrite <- Rinv_mult_distr. + replace 4 with 4. + rewrite Ropp_plus_distr. + reflexivity. + ring. + discrR. + discrR. + reflexivity. + apply Rinv_mult_distr; assumption. +Qed. + +Lemma sin_incr_0 : + forall x y:R, + - (PI / 2) <= x -> + x <= PI / 2 -> - (PI / 2) <= y -> y <= PI / 2 -> sin x <= sin y -> x <= y. +Proof. + intros; case (Rtotal_order (sin x) (sin y)); intro H4; + [ left; apply (sin_increasing_0 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order x y); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (sin_increasing_1 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl (sin y) H8) ] ] + | elim (Rlt_irrefl (sin x) (Rle_lt_trans (sin x) (sin y) (sin x) H3 H5)) ] ]. +Qed. + +Lemma sin_incr_1 : + forall x y:R, + - (PI / 2) <= x -> + x <= PI / 2 -> - (PI / 2) <= y -> y <= PI / 2 -> x <= y -> sin x <= sin y. +Proof. + intros; case (Rtotal_order x y); intro H4; + [ left; apply (sin_increasing_1 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order (sin x) (sin y)); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (sin_increasing_0 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl y H8) ] ] + | elim (Rlt_irrefl x (Rle_lt_trans x y x H3 H5)) ] ]. +Qed. + +Lemma sin_decr_0 : + forall x y:R, + x <= 3 * (PI / 2) -> + PI / 2 <= x -> + y <= 3 * (PI / 2) -> PI / 2 <= y -> sin x <= sin y -> y <= x. +Proof. + intros; case (Rtotal_order (sin x) (sin y)); intro H4; + [ left; apply (sin_decreasing_0 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order x y); intro H6; + [ generalize (sin_decreasing_1 x y H H0 H1 H2 H6); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl (sin y) H8) + | elim H6; intro H7; + [ right; symmetry in |- *; assumption | left; assumption ] ] + | elim (Rlt_irrefl (sin x) (Rle_lt_trans (sin x) (sin y) (sin x) H3 H5)) ] ]. +Qed. + +Lemma sin_decr_1 : + forall x y:R, + x <= 3 * (PI / 2) -> + PI / 2 <= x -> + y <= 3 * (PI / 2) -> PI / 2 <= y -> x <= y -> sin y <= sin x. +Proof. + intros; case (Rtotal_order x y); intro H4; + [ left; apply (sin_decreasing_1 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order (sin x) (sin y)); intro H6; + [ generalize (sin_decreasing_0 x y H H0 H1 H2 H6); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl y H8) + | elim H6; intro H7; + [ right; symmetry in |- *; assumption | left; assumption ] ] + | elim (Rlt_irrefl x (Rle_lt_trans x y x H3 H5)) ] ]. +Qed. + +Lemma cos_incr_0 : + forall x y:R, + PI <= x -> + x <= 2 * PI -> PI <= y -> y <= 2 * PI -> cos x <= cos y -> x <= y. +Proof. + intros; case (Rtotal_order (cos x) (cos y)); intro H4; + [ left; apply (cos_increasing_0 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order x y); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (cos_increasing_1 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl (cos y) H8) ] ] + | elim (Rlt_irrefl (cos x) (Rle_lt_trans (cos x) (cos y) (cos x) H3 H5)) ] ]. +Qed. + +Lemma cos_incr_1 : + forall x y:R, + PI <= x -> + x <= 2 * PI -> PI <= y -> y <= 2 * PI -> x <= y -> cos x <= cos y. +Proof. + intros; case (Rtotal_order x y); intro H4; + [ left; apply (cos_increasing_1 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order (cos x) (cos y)); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (cos_increasing_0 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl y H8) ] ] + | elim (Rlt_irrefl x (Rle_lt_trans x y x H3 H5)) ] ]. +Qed. + +Lemma cos_decr_0 : + forall x y:R, + 0 <= x -> x <= PI -> 0 <= y -> y <= PI -> cos x <= cos y -> y <= x. +Proof. + intros; case (Rtotal_order (cos x) (cos y)); intro H4; + [ left; apply (cos_decreasing_0 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order x y); intro H6; + [ generalize (cos_decreasing_1 x y H H0 H1 H2 H6); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl (cos y) H8) + | elim H6; intro H7; + [ right; symmetry in |- *; assumption | left; assumption ] ] + | elim (Rlt_irrefl (cos x) (Rle_lt_trans (cos x) (cos y) (cos x) H3 H5)) ] ]. +Qed. + +Lemma cos_decr_1 : + forall x y:R, + 0 <= x -> x <= PI -> 0 <= y -> y <= PI -> x <= y -> cos y <= cos x. +Proof. + intros; case (Rtotal_order x y); intro H4; + [ left; apply (cos_decreasing_1 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order (cos x) (cos y)); intro H6; + [ generalize (cos_decreasing_0 x y H H0 H1 H2 H6); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl y H8) + | elim H6; intro H7; + [ right; symmetry in |- *; assumption | left; assumption ] ] + | elim (Rlt_irrefl x (Rle_lt_trans x y x H3 H5)) ] ]. +Qed. + +Lemma tan_incr_0 : + forall x y:R, + - (PI / 4) <= x -> + x <= PI / 4 -> - (PI / 4) <= y -> y <= PI / 4 -> tan x <= tan y -> x <= y. +Proof. + intros; case (Rtotal_order (tan x) (tan y)); intro H4; + [ left; apply (tan_increasing_0 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order x y); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (tan_increasing_1 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl (tan y) H8) ] ] + | elim (Rlt_irrefl (tan x) (Rle_lt_trans (tan x) (tan y) (tan x) H3 H5)) ] ]. +Qed. + +Lemma tan_incr_1 : + forall x y:R, + - (PI / 4) <= x -> + x <= PI / 4 -> - (PI / 4) <= y -> y <= PI / 4 -> x <= y -> tan x <= tan y. +Proof. + intros; case (Rtotal_order x y); intro H4; + [ left; apply (tan_increasing_1 x y H H0 H1 H2 H4) + | elim H4; intro H5; + [ case (Rtotal_order (tan x) (tan y)); intro H6; + [ left; assumption + | elim H6; intro H7; + [ right; assumption + | generalize (tan_increasing_0 y x H1 H2 H H0 H7); intro H8; + rewrite H5 in H8; elim (Rlt_irrefl y H8) ] ] + | elim (Rlt_irrefl x (Rle_lt_trans x y x H3 H5)) ] ]. +Qed. + +(**********) +Lemma sin_eq_0_1 : forall x:R, (exists k : Z, x = IZR k * PI) -> sin x = 0. +Proof. + intros. + elim H; intros. + apply (Zcase_sign x0). + intro. + rewrite H1 in H0. + simpl in H0. + rewrite H0; rewrite Rmult_0_l; apply sin_0. + intro. + cut (0 <= x0)%Z. + intro. + elim (IZN x0 H2); intros. + rewrite H3 in H0. + rewrite <- INR_IZR_INZ in H0. + rewrite H0. + elim (even_odd_cor x1); intros. + elim H4; intro. + rewrite H5. + rewrite mult_INR. + simpl in |- *. + rewrite <- (Rplus_0_l (2 * INR x2 * PI)). + rewrite sin_period. + apply sin_0. + rewrite H5. + rewrite S_INR; rewrite mult_INR. + simpl in |- *. + rewrite Rmult_plus_distr_r. + rewrite Rmult_1_l; rewrite sin_plus. + rewrite sin_PI. + rewrite Rmult_0_r. + rewrite <- (Rplus_0_l (2 * INR x2 * PI)). + rewrite sin_period. + rewrite sin_0; ring. + apply le_IZR. + left; apply IZR_lt. + assert (H2 := Z.gt_lt_iff). + elim (H2 x0 0%Z); intros. + apply H3; assumption. + intro. + rewrite H0. + replace (sin (IZR x0 * PI)) with (- sin (- IZR x0 * PI)). + cut (0 <= - x0)%Z. + intro. + rewrite <- Ropp_Ropp_IZR. + elim (IZN (- x0) H2); intros. + rewrite H3. + rewrite <- INR_IZR_INZ. + elim (even_odd_cor x1); intros. + elim H4; intro. + rewrite H5. + rewrite mult_INR. + simpl in |- *. + rewrite <- (Rplus_0_l (2 * INR x2 * PI)). + rewrite sin_period. + rewrite sin_0; ring. + rewrite H5. + rewrite S_INR; rewrite mult_INR. + simpl in |- *. + rewrite Rmult_plus_distr_r. + rewrite Rmult_1_l; rewrite sin_plus. + rewrite sin_PI. + rewrite Rmult_0_r. + rewrite <- (Rplus_0_l (2 * INR x2 * PI)). + rewrite sin_period. + rewrite sin_0; ring. + apply le_IZR. + apply Rplus_le_reg_l with (IZR x0). + rewrite Rplus_0_r. + rewrite Ropp_Ropp_IZR. + rewrite Rplus_opp_r. + left; replace 0 with (IZR 0); [ apply IZR_lt | reflexivity ]. + assumption. + rewrite <- sin_neg. + rewrite Ropp_mult_distr_l_reverse. + rewrite Ropp_involutive. + reflexivity. +Qed. + +Lemma sin_eq_0_0 (x:R) : sin x = 0 -> exists k : Z, x = IZR k * PI. +Proof. + intros Hx. + destruct (euclidian_division x PI PI_neq0) as (q & r & EQ & Hr & Hr'). + exists q. + rewrite <- (Rplus_0_r (_*_)). subst. apply Rplus_eq_compat_l. + rewrite sin_plus in Hx. + assert (H : sin (IZR q * PI) = 0) by (apply sin_eq_0_1; now exists q). + rewrite H, Rmult_0_l, Rplus_0_l in Hx. + destruct (Rmult_integral _ _ Hx) as [H'|H']. + - exfalso. + generalize (sin2_cos2 (IZR q * PI)). + rewrite H, H', Rsqr_0, Rplus_0_l. + intros; now apply R1_neq_R0. + - rewrite Rabs_right in Hr'; [|left; apply PI_RGT_0]. + destruct Hr as [Hr | ->]; trivial. + exfalso. + generalize (sin_gt_0 r Hr Hr'). rewrite H'. apply Rlt_irrefl. +Qed. + +Lemma cos_eq_0_0 (x:R) : + cos x = 0 -> exists k : Z, x = IZR k * PI + PI / 2. +Proof. + rewrite cos_sin. intros Hx. + destruct (sin_eq_0_0 (PI/2 + x) Hx) as (k,Hk). clear Hx. + exists (k-1)%Z. rewrite <- Z_R_minus; simpl. + symmetry in Hk. field_simplify [Hk]. field. +Qed. + +Lemma cos_eq_0_1 (x:R) : + (exists k : Z, x = IZR k * PI + PI / 2) -> cos x = 0. +Proof. + rewrite cos_sin. intros (k,->). + replace (_ + _) with (IZR k * PI + PI) by field. + rewrite neg_sin, <- Ropp_0. apply Ropp_eq_compat. + apply sin_eq_0_1. now exists k. +Qed. + +Lemma sin_eq_O_2PI_0 (x:R) : + 0 <= x -> x <= 2 * PI -> sin x = 0 -> + x = 0 \/ x = PI \/ x = 2 * PI. +Proof. + intros Lo Hi Hx. destruct (sin_eq_0_0 x Hx) as (k,Hk). clear Hx. + destruct (Rtotal_order PI x) as [Hx|[Hx|Hx]]. + - right; right. + clear Lo. subst. + f_equal. change 2 with (IZR (- (-2))). f_equal. + apply Z.add_move_0_l. + apply one_IZR_lt1. + rewrite plus_IZR; simpl. + split. + + replace (-1) with (-2 + 1) by ring. + apply Rplus_lt_compat_l. + apply Rmult_lt_reg_r with PI; [apply PI_RGT_0|]. + now rewrite Rmult_1_l. + + apply Rle_lt_trans with 0; [|apply Rlt_0_1]. + replace 0 with (-2 + 2) by ring. + apply Rplus_le_compat_l. + apply Rmult_le_reg_r with PI; [apply PI_RGT_0|]. + trivial. + - right; left; auto. + - left. + clear Hi. subst. + replace 0 with (IZR 0 * PI) by (simpl; ring). f_equal. f_equal. + apply one_IZR_lt1. + split. + + apply Rlt_le_trans with 0; + [rewrite <- Ropp_0; apply Ropp_gt_lt_contravar, Rlt_0_1 | ]. + apply Rmult_le_reg_r with PI; [apply PI_RGT_0|]. + now rewrite Rmult_0_l. + + apply Rmult_lt_reg_r with PI; [apply PI_RGT_0|]. + now rewrite Rmult_1_l. +Qed. + +Lemma sin_eq_O_2PI_1 (x:R) : + 0 <= x -> x <= 2 * PI -> + x = 0 \/ x = PI \/ x = 2 * PI -> sin x = 0. +Proof. + intros _ _ [ -> |[ -> | -> ]]. + - now rewrite sin_0. + - now rewrite sin_PI. + - now rewrite sin_2PI. +Qed. + +Lemma cos_eq_0_2PI_0 (x:R) : + 0 <= x -> x <= 2 * PI -> cos x = 0 -> + x = PI / 2 \/ x = 3 * (PI / 2). +Proof. + intros Lo Hi Hx. + destruct (Rtotal_order x (3 * (PI / 2))) as [LT|[EQ|GT]]. + - rewrite cos_sin in Hx. + assert (Lo' : 0 <= PI / 2 + x). + { apply Rplus_le_le_0_compat. apply Rlt_le, PI2_RGT_0. trivial. } + assert (Hi' : PI / 2 + x <= 2 * PI). + { apply Rlt_le. + replace (2 * PI) with (PI / 2 + 3 * (PI / 2)) by field. + now apply Rplus_lt_compat_l. } + destruct (sin_eq_O_2PI_0 (PI / 2 + x) Lo' Hi' Hx) as [H|[H|H]]. + + exfalso. + apply (Rplus_le_compat_l (PI/2)) in Lo. + rewrite Rplus_0_r, H in Lo. + apply (Rlt_irrefl 0 (Rlt_le_trans 0 (PI / 2) 0 PI2_RGT_0 Lo)). + + left. + apply (Rplus_eq_compat_l (-(PI/2))) in H. + ring_simplify in H. rewrite H. field. + + right. + apply (Rplus_eq_compat_l (-(PI/2))) in H. + ring_simplify in H. rewrite H. field. + - now right. + - exfalso. + destruct (cos_eq_0_0 x Hx) as (k,Hk). clear Hx Lo. + subst. + assert (LT : (k < 2)%Z). + { apply lt_IZR. simpl. + apply (Rmult_lt_reg_r PI); [apply PI_RGT_0|]. + apply Rlt_le_trans with (IZR k * PI + PI/2); trivial. + rewrite <- (Rplus_0_r (IZR k * PI)) at 1. + apply Rplus_lt_compat_l. apply PI2_RGT_0. } + assert (GT' : (1 < k)%Z). + { apply lt_IZR. simpl. + apply (Rmult_lt_reg_r PI); [apply PI_RGT_0|rewrite Rmult_1_l]. + replace (3*(PI/2)) with (PI/2 + PI) in GT by field. + rewrite Rplus_comm in GT. + now apply Rplus_lt_reg_r in GT. } + omega. +Qed. + +Lemma cos_eq_0_2PI_1 (x:R) : + 0 <= x -> x <= 2 * PI -> + x = PI / 2 \/ x = 3 * (PI / 2) -> cos x = 0. +Proof. + intros Lo Hi [ -> | -> ]. + - now rewrite cos_PI2. + - now rewrite cos_3PI2. +Qed. |