Proof of Theorem cos2h
Step | Hyp | Ref
| Expression |
1 | | pire 25624 |
. . . . . . 7
⊢ π
∈ ℝ |
2 | 1 | renegcli 11291 |
. . . . . 6
⊢ -π
∈ ℝ |
3 | | iccssre 13170 |
. . . . . 6
⊢ ((-π
∈ ℝ ∧ π ∈ ℝ) → (-π[,]π) ⊆
ℝ) |
4 | 2, 1, 3 | mp2an 689 |
. . . . 5
⊢
(-π[,]π) ⊆ ℝ |
5 | 4 | sseli 3918 |
. . . 4
⊢ (𝐴 ∈ (-π[,]π) →
𝐴 ∈
ℝ) |
6 | 5 | rehalfcld 12229 |
. . 3
⊢ (𝐴 ∈ (-π[,]π) →
(𝐴 / 2) ∈
ℝ) |
7 | 6 | recoscld 15862 |
. 2
⊢ (𝐴 ∈ (-π[,]π) →
(cos‘(𝐴 / 2)) ∈
ℝ) |
8 | | 1re 10984 |
. . . . 5
⊢ 1 ∈
ℝ |
9 | 5 | recoscld 15862 |
. . . . 5
⊢ (𝐴 ∈ (-π[,]π) →
(cos‘𝐴) ∈
ℝ) |
10 | | readdcl 10963 |
. . . . 5
⊢ ((1
∈ ℝ ∧ (cos‘𝐴) ∈ ℝ) → (1 +
(cos‘𝐴)) ∈
ℝ) |
11 | 8, 9, 10 | sylancr 587 |
. . . 4
⊢ (𝐴 ∈ (-π[,]π) → (1
+ (cos‘𝐴)) ∈
ℝ) |
12 | 11 | rehalfcld 12229 |
. . 3
⊢ (𝐴 ∈ (-π[,]π) →
((1 + (cos‘𝐴)) / 2)
∈ ℝ) |
13 | | cosbnd 15899 |
. . . . . 6
⊢ (𝐴 ∈ ℝ → (-1 ≤
(cos‘𝐴) ∧
(cos‘𝐴) ≤
1)) |
14 | 13 | simpld 495 |
. . . . 5
⊢ (𝐴 ∈ ℝ → -1 ≤
(cos‘𝐴)) |
15 | | recoscl 15859 |
. . . . . 6
⊢ (𝐴 ∈ ℝ →
(cos‘𝐴) ∈
ℝ) |
16 | | recn 10970 |
. . . . . . . . 9
⊢
((cos‘𝐴)
∈ ℝ → (cos‘𝐴) ∈ ℂ) |
17 | | recn 10970 |
. . . . . . . . 9
⊢ (1 ∈
ℝ → 1 ∈ ℂ) |
18 | | subneg 11279 |
. . . . . . . . . 10
⊢
(((cos‘𝐴)
∈ ℂ ∧ 1 ∈ ℂ) → ((cos‘𝐴) − -1) = ((cos‘𝐴) + 1)) |
19 | | addcom 11170 |
. . . . . . . . . . 11
⊢ ((1
∈ ℂ ∧ (cos‘𝐴) ∈ ℂ) → (1 +
(cos‘𝐴)) =
((cos‘𝐴) +
1)) |
20 | 19 | ancoms 459 |
. . . . . . . . . 10
⊢
(((cos‘𝐴)
∈ ℂ ∧ 1 ∈ ℂ) → (1 + (cos‘𝐴)) = ((cos‘𝐴) + 1)) |
21 | 18, 20 | eqtr4d 2782 |
. . . . . . . . 9
⊢
(((cos‘𝐴)
∈ ℂ ∧ 1 ∈ ℂ) → ((cos‘𝐴) − -1) = (1 + (cos‘𝐴))) |
22 | 16, 17, 21 | syl2an 596 |
. . . . . . . 8
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → ((cos‘𝐴) − -1) = (1 + (cos‘𝐴))) |
23 | 22 | breq2d 5087 |
. . . . . . 7
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → (0 ≤ ((cos‘𝐴) − -1) ↔ 0 ≤ (1 +
(cos‘𝐴)))) |
24 | | renegcl 11293 |
. . . . . . . 8
⊢ (1 ∈
ℝ → -1 ∈ ℝ) |
25 | | subge0 11497 |
. . . . . . . 8
⊢
(((cos‘𝐴)
∈ ℝ ∧ -1 ∈ ℝ) → (0 ≤ ((cos‘𝐴) − -1) ↔ -1 ≤
(cos‘𝐴))) |
26 | 24, 25 | sylan2 593 |
. . . . . . 7
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → (0 ≤ ((cos‘𝐴) − -1) ↔ -1 ≤
(cos‘𝐴))) |
27 | 10 | ancoms 459 |
. . . . . . . 8
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → (1 + (cos‘𝐴)) ∈ ℝ) |
28 | | halfnneg2 12213 |
. . . . . . . 8
⊢ ((1 +
(cos‘𝐴)) ∈
ℝ → (0 ≤ (1 + (cos‘𝐴)) ↔ 0 ≤ ((1 + (cos‘𝐴)) / 2))) |
29 | 27, 28 | syl 17 |
. . . . . . 7
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → (0 ≤ (1 + (cos‘𝐴)) ↔ 0 ≤ ((1 +
(cos‘𝐴)) /
2))) |
30 | 23, 26, 29 | 3bitr3d 309 |
. . . . . 6
⊢
(((cos‘𝐴)
∈ ℝ ∧ 1 ∈ ℝ) → (-1 ≤ (cos‘𝐴) ↔ 0 ≤ ((1 +
(cos‘𝐴)) /
2))) |
31 | 15, 8, 30 | sylancl 586 |
. . . . 5
⊢ (𝐴 ∈ ℝ → (-1 ≤
(cos‘𝐴) ↔ 0 ≤
((1 + (cos‘𝐴)) /
2))) |
32 | 14, 31 | mpbid 231 |
. . . 4
⊢ (𝐴 ∈ ℝ → 0 ≤
((1 + (cos‘𝐴)) /
2)) |
33 | 5, 32 | syl 17 |
. . 3
⊢ (𝐴 ∈ (-π[,]π) → 0
≤ ((1 + (cos‘𝐴)) /
2)) |
34 | 12, 33 | resqrtcld 15138 |
. 2
⊢ (𝐴 ∈ (-π[,]π) →
(√‘((1 + (cos‘𝐴)) / 2)) ∈ ℝ) |
35 | 2, 1 | elicc2i 13154 |
. . . 4
⊢ (𝐴 ∈ (-π[,]π) ↔
(𝐴 ∈ ℝ ∧
-π ≤ 𝐴 ∧ 𝐴 ≤ π)) |
36 | | 2re 12056 |
. . . . . . . . . . 11
⊢ 2 ∈
ℝ |
37 | | 2pos 12085 |
. . . . . . . . . . 11
⊢ 0 <
2 |
38 | 36, 37 | pm3.2i 471 |
. . . . . . . . . 10
⊢ (2 ∈
ℝ ∧ 0 < 2) |
39 | | lediv1 11849 |
. . . . . . . . . 10
⊢ ((-π
∈ ℝ ∧ 𝐴
∈ ℝ ∧ (2 ∈ ℝ ∧ 0 < 2)) → (-π ≤
𝐴 ↔ (-π / 2) ≤
(𝐴 / 2))) |
40 | 2, 38, 39 | mp3an13 1451 |
. . . . . . . . 9
⊢ (𝐴 ∈ ℝ → (-π
≤ 𝐴 ↔ (-π / 2)
≤ (𝐴 /
2))) |
41 | | picn 25625 |
. . . . . . . . . . 11
⊢ π
∈ ℂ |
42 | | 2cn 12057 |
. . . . . . . . . . 11
⊢ 2 ∈
ℂ |
43 | | 2ne0 12086 |
. . . . . . . . . . 11
⊢ 2 ≠
0 |
44 | | divneg 11676 |
. . . . . . . . . . 11
⊢ ((π
∈ ℂ ∧ 2 ∈ ℂ ∧ 2 ≠ 0) → -(π / 2) =
(-π / 2)) |
45 | 41, 42, 43, 44 | mp3an 1460 |
. . . . . . . . . 10
⊢ -(π /
2) = (-π / 2) |
46 | 45 | breq1i 5082 |
. . . . . . . . 9
⊢ (-(π /
2) ≤ (𝐴 / 2) ↔
(-π / 2) ≤ (𝐴 /
2)) |
47 | 40, 46 | bitr4di 289 |
. . . . . . . 8
⊢ (𝐴 ∈ ℝ → (-π
≤ 𝐴 ↔ -(π / 2)
≤ (𝐴 /
2))) |
48 | | lediv1 11849 |
. . . . . . . . 9
⊢ ((𝐴 ∈ ℝ ∧ π
∈ ℝ ∧ (2 ∈ ℝ ∧ 0 < 2)) → (𝐴 ≤ π ↔ (𝐴 / 2) ≤ (π /
2))) |
49 | 1, 38, 48 | mp3an23 1452 |
. . . . . . . 8
⊢ (𝐴 ∈ ℝ → (𝐴 ≤ π ↔ (𝐴 / 2) ≤ (π /
2))) |
50 | 47, 49 | anbi12d 631 |
. . . . . . 7
⊢ (𝐴 ∈ ℝ → ((-π
≤ 𝐴 ∧ 𝐴 ≤ π) ↔ (-(π / 2)
≤ (𝐴 / 2) ∧ (𝐴 / 2) ≤ (π /
2)))) |
51 | | rehalfcl 12208 |
. . . . . . . . 9
⊢ (𝐴 ∈ ℝ → (𝐴 / 2) ∈
ℝ) |
52 | 51 | rexrd 11034 |
. . . . . . . 8
⊢ (𝐴 ∈ ℝ → (𝐴 / 2) ∈
ℝ*) |
53 | | halfpire 25630 |
. . . . . . . . . . 11
⊢ (π /
2) ∈ ℝ |
54 | 53 | renegcli 11291 |
. . . . . . . . . 10
⊢ -(π /
2) ∈ ℝ |
55 | 54 | rexri 11042 |
. . . . . . . . 9
⊢ -(π /
2) ∈ ℝ* |
56 | 53 | rexri 11042 |
. . . . . . . . 9
⊢ (π /
2) ∈ ℝ* |
57 | | elicc4 13155 |
. . . . . . . . 9
⊢ ((-(π
/ 2) ∈ ℝ* ∧ (π / 2) ∈ ℝ*
∧ (𝐴 / 2) ∈
ℝ*) → ((𝐴 / 2) ∈ (-(π / 2)[,](π / 2))
↔ (-(π / 2) ≤ (𝐴
/ 2) ∧ (𝐴 / 2) ≤
(π / 2)))) |
58 | 55, 56, 57 | mp3an12 1450 |
. . . . . . . 8
⊢ ((𝐴 / 2) ∈ ℝ*
→ ((𝐴 / 2) ∈
(-(π / 2)[,](π / 2)) ↔ (-(π / 2) ≤ (𝐴 / 2) ∧ (𝐴 / 2) ≤ (π / 2)))) |
59 | 52, 58 | syl 17 |
. . . . . . 7
⊢ (𝐴 ∈ ℝ → ((𝐴 / 2) ∈ (-(π /
2)[,](π / 2)) ↔ (-(π / 2) ≤ (𝐴 / 2) ∧ (𝐴 / 2) ≤ (π / 2)))) |
60 | 50, 59 | bitr4d 281 |
. . . . . 6
⊢ (𝐴 ∈ ℝ → ((-π
≤ 𝐴 ∧ 𝐴 ≤ π) ↔ (𝐴 / 2) ∈ (-(π /
2)[,](π / 2)))) |
61 | 60 | biimpd 228 |
. . . . 5
⊢ (𝐴 ∈ ℝ → ((-π
≤ 𝐴 ∧ 𝐴 ≤ π) → (𝐴 / 2) ∈ (-(π /
2)[,](π / 2)))) |
62 | 61 | 3impib 1115 |
. . . 4
⊢ ((𝐴 ∈ ℝ ∧ -π ≤
𝐴 ∧ 𝐴 ≤ π) → (𝐴 / 2) ∈ (-(π / 2)[,](π /
2))) |
63 | 35, 62 | sylbi 216 |
. . 3
⊢ (𝐴 ∈ (-π[,]π) →
(𝐴 / 2) ∈ (-(π /
2)[,](π / 2))) |
64 | | cosq14ge0 25677 |
. . 3
⊢ ((𝐴 / 2) ∈ (-(π /
2)[,](π / 2)) → 0 ≤ (cos‘(𝐴 / 2))) |
65 | 63, 64 | syl 17 |
. 2
⊢ (𝐴 ∈ (-π[,]π) → 0
≤ (cos‘(𝐴 /
2))) |
66 | 12, 33 | sqrtge0d 15141 |
. 2
⊢ (𝐴 ∈ (-π[,]π) → 0
≤ (√‘((1 + (cos‘𝐴)) / 2))) |
67 | 5 | recnd 11012 |
. . 3
⊢ (𝐴 ∈ (-π[,]π) →
𝐴 ∈
ℂ) |
68 | | ax-1cn 10938 |
. . . . . . 7
⊢ 1 ∈
ℂ |
69 | | coscl 15845 |
. . . . . . 7
⊢ (𝐴 ∈ ℂ →
(cos‘𝐴) ∈
ℂ) |
70 | | addcl 10962 |
. . . . . . 7
⊢ ((1
∈ ℂ ∧ (cos‘𝐴) ∈ ℂ) → (1 +
(cos‘𝐴)) ∈
ℂ) |
71 | 68, 69, 70 | sylancr 587 |
. . . . . 6
⊢ (𝐴 ∈ ℂ → (1 +
(cos‘𝐴)) ∈
ℂ) |
72 | 71 | halfcld 12227 |
. . . . 5
⊢ (𝐴 ∈ ℂ → ((1 +
(cos‘𝐴)) / 2) ∈
ℂ) |
73 | 72 | sqsqrtd 15160 |
. . . 4
⊢ (𝐴 ∈ ℂ →
((√‘((1 + (cos‘𝐴)) / 2))↑2) = ((1 + (cos‘𝐴)) / 2)) |
74 | | divcan2 11650 |
. . . . . . . . 9
⊢ ((𝐴 ∈ ℂ ∧ 2 ∈
ℂ ∧ 2 ≠ 0) → (2 · (𝐴 / 2)) = 𝐴) |
75 | 42, 43, 74 | mp3an23 1452 |
. . . . . . . 8
⊢ (𝐴 ∈ ℂ → (2
· (𝐴 / 2)) = 𝐴) |
76 | 75 | fveq2d 6787 |
. . . . . . 7
⊢ (𝐴 ∈ ℂ →
(cos‘(2 · (𝐴 /
2))) = (cos‘𝐴)) |
77 | | halfcl 12207 |
. . . . . . . 8
⊢ (𝐴 ∈ ℂ → (𝐴 / 2) ∈
ℂ) |
78 | | cos2t 15896 |
. . . . . . . 8
⊢ ((𝐴 / 2) ∈ ℂ →
(cos‘(2 · (𝐴 /
2))) = ((2 · ((cos‘(𝐴 / 2))↑2)) − 1)) |
79 | 77, 78 | syl 17 |
. . . . . . 7
⊢ (𝐴 ∈ ℂ →
(cos‘(2 · (𝐴 /
2))) = ((2 · ((cos‘(𝐴 / 2))↑2)) − 1)) |
80 | 76, 79 | eqtr3d 2781 |
. . . . . 6
⊢ (𝐴 ∈ ℂ →
(cos‘𝐴) = ((2
· ((cos‘(𝐴 /
2))↑2)) − 1)) |
81 | 80 | oveq2d 7300 |
. . . . 5
⊢ (𝐴 ∈ ℂ → (1 +
(cos‘𝐴)) = (1 + ((2
· ((cos‘(𝐴 /
2))↑2)) − 1))) |
82 | 81 | oveq1d 7299 |
. . . 4
⊢ (𝐴 ∈ ℂ → ((1 +
(cos‘𝐴)) / 2) = ((1 +
((2 · ((cos‘(𝐴
/ 2))↑2)) − 1)) / 2)) |
83 | 77 | coscld 15849 |
. . . . . 6
⊢ (𝐴 ∈ ℂ →
(cos‘(𝐴 / 2)) ∈
ℂ) |
84 | 83 | sqcld 13871 |
. . . . 5
⊢ (𝐴 ∈ ℂ →
((cos‘(𝐴 /
2))↑2) ∈ ℂ) |
85 | | mulcl 10964 |
. . . . . . . . 9
⊢ ((2
∈ ℂ ∧ ((cos‘(𝐴 / 2))↑2) ∈ ℂ) → (2
· ((cos‘(𝐴 /
2))↑2)) ∈ ℂ) |
86 | 42, 85 | mpan 687 |
. . . . . . . 8
⊢
(((cos‘(𝐴 /
2))↑2) ∈ ℂ → (2 · ((cos‘(𝐴 / 2))↑2)) ∈
ℂ) |
87 | | pncan3 11238 |
. . . . . . . 8
⊢ ((1
∈ ℂ ∧ (2 · ((cos‘(𝐴 / 2))↑2)) ∈ ℂ) → (1 +
((2 · ((cos‘(𝐴
/ 2))↑2)) − 1)) = (2 · ((cos‘(𝐴 / 2))↑2))) |
88 | 68, 86, 87 | sylancr 587 |
. . . . . . 7
⊢
(((cos‘(𝐴 /
2))↑2) ∈ ℂ → (1 + ((2 · ((cos‘(𝐴 / 2))↑2)) − 1)) = (2
· ((cos‘(𝐴 /
2))↑2))) |
89 | 88 | oveq1d 7299 |
. . . . . 6
⊢
(((cos‘(𝐴 /
2))↑2) ∈ ℂ → ((1 + ((2 · ((cos‘(𝐴 / 2))↑2)) − 1)) / 2)
= ((2 · ((cos‘(𝐴 / 2))↑2)) / 2)) |
90 | | divcan3 11668 |
. . . . . . 7
⊢
((((cos‘(𝐴 /
2))↑2) ∈ ℂ ∧ 2 ∈ ℂ ∧ 2 ≠ 0) → ((2
· ((cos‘(𝐴 /
2))↑2)) / 2) = ((cos‘(𝐴 / 2))↑2)) |
91 | 42, 43, 90 | mp3an23 1452 |
. . . . . 6
⊢
(((cos‘(𝐴 /
2))↑2) ∈ ℂ → ((2 · ((cos‘(𝐴 / 2))↑2)) / 2) = ((cos‘(𝐴 / 2))↑2)) |
92 | 89, 91 | eqtrd 2779 |
. . . . 5
⊢
(((cos‘(𝐴 /
2))↑2) ∈ ℂ → ((1 + ((2 · ((cos‘(𝐴 / 2))↑2)) − 1)) / 2)
= ((cos‘(𝐴 /
2))↑2)) |
93 | 84, 92 | syl 17 |
. . . 4
⊢ (𝐴 ∈ ℂ → ((1 + ((2
· ((cos‘(𝐴 /
2))↑2)) − 1)) / 2) = ((cos‘(𝐴 / 2))↑2)) |
94 | 73, 82, 93 | 3eqtrrd 2784 |
. . 3
⊢ (𝐴 ∈ ℂ →
((cos‘(𝐴 /
2))↑2) = ((√‘((1 + (cos‘𝐴)) / 2))↑2)) |
95 | 67, 94 | syl 17 |
. 2
⊢ (𝐴 ∈ (-π[,]π) →
((cos‘(𝐴 /
2))↑2) = ((√‘((1 + (cos‘𝐴)) / 2))↑2)) |
96 | 7, 34, 65, 66, 95 | sq11d 13984 |
1
⊢ (𝐴 ∈ (-π[,]π) →
(cos‘(𝐴 / 2)) =
(√‘((1 + (cos‘𝐴)) / 2))) |