cos2t - Intuitionistic Logic Explorer

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Theorem cos2t 12136

Description: Double-angle formula for cosine. (Contributed by Paul Chapman, 24-Jan-2008.)

**Assertion**
Ref	Expression
cos2t	⊢ (𝐴 ∈ ℂ → (cos‘(2 · 𝐴)) = ((2 · ((cos‘𝐴)↑2)) − 1))

**Proof of Theorem cos2t**
Step	Hyp	Ref	Expression
1		coscl 12093	. . . 4 ⊢ (𝐴 ∈ ℂ → (cos‘𝐴) ∈ ℂ)
2	1	sqcld 10838	. . 3 ⊢ (𝐴 ∈ ℂ → ((cos‘𝐴)↑2) ∈ ℂ)
3		ax-1cn 8038	. . . 4 ⊢ 1 ∈ ℂ
4		subsub3 8324	. . . 4 ⊢ ((((cos‘𝐴)↑2) ∈ ℂ ∧ 1 ∈ ℂ ∧ ((cos‘𝐴)↑2) ∈ ℂ) → (((cos‘𝐴)↑2) − (1 − ((cos‘𝐴)↑2))) = ((((cos‘𝐴)↑2) + ((cos‘𝐴)↑2)) − 1))
5	3, 4	mp3an2 1338	. . 3 ⊢ ((((cos‘𝐴)↑2) ∈ ℂ ∧ ((cos‘𝐴)↑2) ∈ ℂ) → (((cos‘𝐴)↑2) − (1 − ((cos‘𝐴)↑2))) = ((((cos‘𝐴)↑2) + ((cos‘𝐴)↑2)) − 1))
6	2, 2, 5	syl2anc 411	. 2 ⊢ (𝐴 ∈ ℂ → (((cos‘𝐴)↑2) − (1 − ((cos‘𝐴)↑2))) = ((((cos‘𝐴)↑2) + ((cos‘𝐴)↑2)) − 1))
7		cosadd 12123	. . . . 5 ⊢ ((𝐴 ∈ ℂ ∧ 𝐴 ∈ ℂ) → (cos‘(𝐴 + 𝐴)) = (((cos‘𝐴) · (cos‘𝐴)) − ((sin‘𝐴) · (sin‘𝐴))))
8	7	anidms 397	. . . 4 ⊢ (𝐴 ∈ ℂ → (cos‘(𝐴 + 𝐴)) = (((cos‘𝐴) · (cos‘𝐴)) − ((sin‘𝐴) · (sin‘𝐴))))
9		2times 9184	. . . . 5 ⊢ (𝐴 ∈ ℂ → (2 · 𝐴) = (𝐴 + 𝐴))
10	9	fveq2d 5593	. . . 4 ⊢ (𝐴 ∈ ℂ → (cos‘(2 · 𝐴)) = (cos‘(𝐴 + 𝐴)))
11	1	sqvald 10837	. . . . 5 ⊢ (𝐴 ∈ ℂ → ((cos‘𝐴)↑2) = ((cos‘𝐴) · (cos‘𝐴)))
12		sincl 12092	. . . . . 6 ⊢ (𝐴 ∈ ℂ → (sin‘𝐴) ∈ ℂ)
13	12	sqvald 10837	. . . . 5 ⊢ (𝐴 ∈ ℂ → ((sin‘𝐴)↑2) = ((sin‘𝐴) · (sin‘𝐴)))
14	11, 13	oveq12d 5975	. . . 4 ⊢ (𝐴 ∈ ℂ → (((cos‘𝐴)↑2) − ((sin‘𝐴)↑2)) = (((cos‘𝐴) · (cos‘𝐴)) − ((sin‘𝐴) · (sin‘𝐴))))
15	8, 10, 14	3eqtr4d 2249	. . 3 ⊢ (𝐴 ∈ ℂ → (cos‘(2 · 𝐴)) = (((cos‘𝐴)↑2) − ((sin‘𝐴)↑2)))
16	12	sqcld 10838	. . . . . . 7 ⊢ (𝐴 ∈ ℂ → ((sin‘𝐴)↑2) ∈ ℂ)
17	16, 2	addcomd 8243	. . . . . 6 ⊢ (𝐴 ∈ ℂ → (((sin‘𝐴)↑2) + ((cos‘𝐴)↑2)) = (((cos‘𝐴)↑2) + ((sin‘𝐴)↑2)))
18		sincossq 12134	. . . . . 6 ⊢ (𝐴 ∈ ℂ → (((sin‘𝐴)↑2) + ((cos‘𝐴)↑2)) = 1)
19	17, 18	eqtr3d 2241	. . . . 5 ⊢ (𝐴 ∈ ℂ → (((cos‘𝐴)↑2) + ((sin‘𝐴)↑2)) = 1)
20		subadd 8295	. . . . . . 7 ⊢ ((1 ∈ ℂ ∧ ((cos‘𝐴)↑2) ∈ ℂ ∧ ((sin‘𝐴)↑2) ∈ ℂ) → ((1 − ((cos‘𝐴)↑2)) = ((sin‘𝐴)↑2) ↔ (((cos‘𝐴)↑2) + ((sin‘𝐴)↑2)) = 1))
21	3, 20	mp3an1 1337	. . . . . 6 ⊢ ((((cos‘𝐴)↑2) ∈ ℂ ∧ ((sin‘𝐴)↑2) ∈ ℂ) → ((1 − ((cos‘𝐴)↑2)) = ((sin‘𝐴)↑2) ↔ (((cos‘𝐴)↑2) + ((sin‘𝐴)↑2)) = 1))
22	2, 16, 21	syl2anc 411	. . . . 5 ⊢ (𝐴 ∈ ℂ → ((1 − ((cos‘𝐴)↑2)) = ((sin‘𝐴)↑2) ↔ (((cos‘𝐴)↑2) + ((sin‘𝐴)↑2)) = 1))
23	19, 22	mpbird 167	. . . 4 ⊢ (𝐴 ∈ ℂ → (1 − ((cos‘𝐴)↑2)) = ((sin‘𝐴)↑2))
24	23	oveq2d 5973	. . 3 ⊢ (𝐴 ∈ ℂ → (((cos‘𝐴)↑2) − (1 − ((cos‘𝐴)↑2))) = (((cos‘𝐴)↑2) − ((sin‘𝐴)↑2)))
25	15, 24	eqtr4d 2242	. 2 ⊢ (𝐴 ∈ ℂ → (cos‘(2 · 𝐴)) = (((cos‘𝐴)↑2) − (1 − ((cos‘𝐴)↑2))))
26	2	2timesd 9300	. . 3 ⊢ (𝐴 ∈ ℂ → (2 · ((cos‘𝐴)↑2)) = (((cos‘𝐴)↑2) + ((cos‘𝐴)↑2)))
27	26	oveq1d 5972	. 2 ⊢ (𝐴 ∈ ℂ → ((2 · ((cos‘𝐴)↑2)) − 1) = ((((cos‘𝐴)↑2) + ((cos‘𝐴)↑2)) − 1))
28	6, 25, 27	3eqtr4d 2249	1 ⊢ (𝐴 ∈ ℂ → (cos‘(2 · 𝐴)) = ((2 · ((cos‘𝐴)↑2)) − 1))

Colors of variables: wff set class

Syntax hints: → wi 4 ↔ wb 105 = wceq 1373 ∈ wcel 2177 ‘cfv 5280 (class class class)co 5957 ℂcc 7943 1c1 7946 + caddc 7948 · cmul 7950 − cmin 8263 2c2 9107 ↑cexp 10705 sincsin 12030 cosccos 12031

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 106 ax-ia2 107 ax-ia3 108 ax-in1 615 ax-in2 616 ax-io 711 ax-5 1471 ax-7 1472 ax-gen 1473 ax-ie1 1517 ax-ie2 1518 ax-8 1528 ax-10 1529 ax-11 1530 ax-i12 1531 ax-bndl 1533 ax-4 1534 ax-17 1550 ax-i9 1554 ax-ial 1558 ax-i5r 1559 ax-13 2179 ax-14 2180 ax-ext 2188 ax-coll 4167 ax-sep 4170 ax-nul 4178 ax-pow 4226 ax-pr 4261 ax-un 4488 ax-setind 4593 ax-iinf 4644 ax-cnex 8036 ax-resscn 8037 ax-1cn 8038 ax-1re 8039 ax-icn 8040 ax-addcl 8041 ax-addrcl 8042 ax-mulcl 8043 ax-mulrcl 8044 ax-addcom 8045 ax-mulcom 8046 ax-addass 8047 ax-mulass 8048 ax-distr 8049 ax-i2m1 8050 ax-0lt1 8051 ax-1rid 8052 ax-0id 8053 ax-rnegex 8054 ax-precex 8055 ax-cnre 8056 ax-pre-ltirr 8057 ax-pre-ltwlin 8058 ax-pre-lttrn 8059 ax-pre-apti 8060 ax-pre-ltadd 8061 ax-pre-mulgt0 8062 ax-pre-mulext 8063 ax-arch 8064 ax-caucvg 8065

This theorem depends on definitions: df-bi 117 df-dc 837 df-3or 982 df-3an 983 df-tru 1376 df-fal 1379 df-nf 1485 df-sb 1787 df-eu 2058 df-mo 2059 df-clab 2193 df-cleq 2199 df-clel 2202 df-nfc 2338 df-ne 2378 df-nel 2473 df-ral 2490 df-rex 2491 df-reu 2492 df-rmo 2493 df-rab 2494 df-v 2775 df-sbc 3003 df-csb 3098 df-dif 3172 df-un 3174 df-in 3176 df-ss 3183 df-nul 3465 df-if 3576 df-pw 3623 df-sn 3644 df-pr 3645 df-op 3647 df-uni 3857 df-int 3892 df-iun 3935 df-disj 4028 df-br 4052 df-opab 4114 df-mpt 4115 df-tr 4151 df-id 4348 df-po 4351 df-iso 4352 df-iord 4421 df-on 4423 df-ilim 4424 df-suc 4426 df-iom 4647 df-xp 4689 df-rel 4690 df-cnv 4691 df-co 4692 df-dm 4693 df-rn 4694 df-res 4695 df-ima 4696 df-iota 5241 df-fun 5282 df-fn 5283 df-f 5284 df-f1 5285 df-fo 5286 df-f1o 5287 df-fv 5288 df-isom 5289 df-riota 5912 df-ov 5960 df-oprab 5961 df-mpo 5962 df-1st 6239 df-2nd 6240 df-recs 6404 df-irdg 6469 df-frec 6490 df-1o 6515 df-oadd 6519 df-er 6633 df-en 6841 df-dom 6842 df-fin 6843 df-sup 7101 df-pnf 8129 df-mnf 8130 df-xr 8131 df-ltxr 8132 df-le 8133 df-sub 8265 df-neg 8266 df-reap 8668 df-ap 8675 df-div 8766 df-inn 9057 df-2 9115 df-3 9116 df-4 9117 df-n0 9316 df-z 9393 df-uz 9669 df-q 9761 df-rp 9796 df-ico 10036 df-fz 10151 df-fzo 10285 df-seqfrec 10615 df-exp 10706 df-fac 10893 df-bc 10915 df-ihash 10943 df-cj 11228 df-re 11229 df-im 11230 df-rsqrt 11384 df-abs 11385 df-clim 11665 df-sumdc 11740 df-ef 12034 df-sin 12036 df-cos 12037

This theorem is referenced by: cos2tsin 12137 cos2bnd 12146 sin0pilem1 15328 cospi 15347 cos2pi 15351 tangtx 15385 coskpi 15395

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