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Theorem coskpi 26460

Description: The absolute value of the cosine of an integer multiple of π is 1. (Contributed by NM, 19-Aug-2008.)

**Assertion**
Ref	Expression
coskpi	⊢ (𝐾 ∈ ℤ → (abs‘(cos‘(𝐾 · π))) = 1)

**Proof of Theorem coskpi**
Step	Hyp	Ref	Expression
1		zcn 12480	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → 𝐾 ∈ ℂ)
2		2cn 12207	. . . . . . . . . . 11 ⊢ 2 ∈ ℂ
3		picn 26395	. . . . . . . . . . 11 ⊢ π ∈ ℂ
4		mul12 11285	. . . . . . . . . . 11 ⊢ ((𝐾 ∈ ℂ ∧ 2 ∈ ℂ ∧ π ∈ ℂ) → (𝐾 · (2 · π)) = (2 · (𝐾 · π)))
5	2, 3, 4	mp3an23 1455	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℂ → (𝐾 · (2 · π)) = (2 · (𝐾 · π)))
6	1, 5	syl 17	. . . . . . . . 9 ⊢ (𝐾 ∈ ℤ → (𝐾 · (2 · π)) = (2 · (𝐾 · π)))
7	6	fveq2d 6832	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · (2 · π))) = (cos‘(2 · (𝐾 · π))))
8		cos2kpi 26421	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · (2 · π))) = 1)
9		zre 12479	. . . . . . . . . . 11 ⊢ (𝐾 ∈ ℤ → 𝐾 ∈ ℝ)
10		pire 26394	. . . . . . . . . . 11 ⊢ π ∈ ℝ
11		remulcl 11098	. . . . . . . . . . 11 ⊢ ((𝐾 ∈ ℝ ∧ π ∈ ℝ) → (𝐾 · π) ∈ ℝ)
12	9, 10, 11	sylancl 586	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → (𝐾 · π) ∈ ℝ)
13	12	recnd 11147	. . . . . . . . 9 ⊢ (𝐾 ∈ ℤ → (𝐾 · π) ∈ ℂ)
14		cos2t 16089	. . . . . . . . 9 ⊢ ((𝐾 · π) ∈ ℂ → (cos‘(2 · (𝐾 · π))) = ((2 · ((cos‘(𝐾 · π))↑2)) − 1))
15	13, 14	syl 17	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (cos‘(2 · (𝐾 · π))) = ((2 · ((cos‘(𝐾 · π))↑2)) − 1))
16	7, 8, 15	3eqtr3rd 2777	. . . . . . 7 ⊢ (𝐾 ∈ ℤ → ((2 · ((cos‘(𝐾 · π))↑2)) − 1) = 1)
17	12	recoscld 16055	. . . . . . . . . . 11 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · π)) ∈ ℝ)
18	17	recnd 11147	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · π)) ∈ ℂ)
19	18	sqcld 14053	. . . . . . . . 9 ⊢ (𝐾 ∈ ℤ → ((cos‘(𝐾 · π))↑2) ∈ ℂ)
20		mulcl 11097	. . . . . . . . 9 ⊢ ((2 ∈ ℂ ∧ ((cos‘(𝐾 · π))↑2) ∈ ℂ) → (2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ)
21	2, 19, 20	sylancr 587	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ)
22		ax-1cn 11071	. . . . . . . . 9 ⊢ 1 ∈ ℂ
23		subadd 11370	. . . . . . . . 9 ⊢ (((2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ ∧ 1 ∈ ℂ ∧ 1 ∈ ℂ) → (((2 · ((cos‘(𝐾 · π))↑2)) − 1) = 1 ↔ (1 + 1) = (2 · ((cos‘(𝐾 · π))↑2))))
24	22, 22, 23	mp3an23 1455	. . . . . . . 8 ⊢ ((2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ → (((2 · ((cos‘(𝐾 · π))↑2)) − 1) = 1 ↔ (1 + 1) = (2 · ((cos‘(𝐾 · π))↑2))))
25	21, 24	syl 17	. . . . . . 7 ⊢ (𝐾 ∈ ℤ → (((2 · ((cos‘(𝐾 · π))↑2)) − 1) = 1 ↔ (1 + 1) = (2 · ((cos‘(𝐾 · π))↑2))))
26	16, 25	mpbid 232	. . . . . 6 ⊢ (𝐾 ∈ ℤ → (1 + 1) = (2 · ((cos‘(𝐾 · π))↑2)))
27		2t1e2 12290	. . . . . . 7 ⊢ (2 · 1) = 2
28		df-2 12195	. . . . . . 7 ⊢ 2 = (1 + 1)
29	27, 28	eqtr2i 2757	. . . . . 6 ⊢ (1 + 1) = (2 · 1)
30	26, 29	eqtr3di 2783	. . . . 5 ⊢ (𝐾 ∈ ℤ → (2 · ((cos‘(𝐾 · π))↑2)) = (2 · 1))
31		2cnne0 12337	. . . . . . 7 ⊢ (2 ∈ ℂ ∧ 2 ≠ 0)
32		mulcan 11761	. . . . . . 7 ⊢ ((((cos‘(𝐾 · π))↑2) ∈ ℂ ∧ 1 ∈ ℂ ∧ (2 ∈ ℂ ∧ 2 ≠ 0)) → ((2 · ((cos‘(𝐾 · π))↑2)) = (2 · 1) ↔ ((cos‘(𝐾 · π))↑2) = 1))
33	22, 31, 32	mp3an23 1455	. . . . . 6 ⊢ (((cos‘(𝐾 · π))↑2) ∈ ℂ → ((2 · ((cos‘(𝐾 · π))↑2)) = (2 · 1) ↔ ((cos‘(𝐾 · π))↑2) = 1))
34	19, 33	syl 17	. . . . 5 ⊢ (𝐾 ∈ ℤ → ((2 · ((cos‘(𝐾 · π))↑2)) = (2 · 1) ↔ ((cos‘(𝐾 · π))↑2) = 1))
35	30, 34	mpbid 232	. . . 4 ⊢ (𝐾 ∈ ℤ → ((cos‘(𝐾 · π))↑2) = 1)
36		sq1 14104	. . . 4 ⊢ (1↑2) = 1
37	35, 36	eqtr4di 2786	. . 3 ⊢ (𝐾 ∈ ℤ → ((cos‘(𝐾 · π))↑2) = (1↑2))
38		1re 11119	. . . 4 ⊢ 1 ∈ ℝ
39		sqabs 15216	. . . 4 ⊢ (((cos‘(𝐾 · π)) ∈ ℝ ∧ 1 ∈ ℝ) → (((cos‘(𝐾 · π))↑2) = (1↑2) ↔ (abs‘(cos‘(𝐾 · π))) = (abs‘1)))
40	17, 38, 39	sylancl 586	. . 3 ⊢ (𝐾 ∈ ℤ → (((cos‘(𝐾 · π))↑2) = (1↑2) ↔ (abs‘(cos‘(𝐾 · π))) = (abs‘1)))
41	37, 40	mpbid 232	. 2 ⊢ (𝐾 ∈ ℤ → (abs‘(cos‘(𝐾 · π))) = (abs‘1))
42		abs1 15206	. 2 ⊢ (abs‘1) = 1
43	41, 42	eqtrdi 2784	1 ⊢ (𝐾 ∈ ℤ → (abs‘(cos‘(𝐾 · π))) = 1)

Colors of variables: wff setvar class

Syntax hints: → wi 4 ↔ wb 206 ∧ wa 395 = wceq 1541 ∈ wcel 2113 ≠ wne 2929 ‘cfv 6486 (class class class)co 7352 ℂcc 11011 ℝcr 11012 0cc0 11013 1c1 11014 + caddc 11016 · cmul 11018 − cmin 11351 2c2 12187 ℤcz 12475 ↑cexp 13970 abscabs 15143 cosccos 15973 πcpi 15975

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1911 ax-6 1968 ax-7 2009 ax-8 2115 ax-9 2123 ax-10 2146 ax-11 2162 ax-12 2182 ax-ext 2705 ax-rep 5219 ax-sep 5236 ax-nul 5246 ax-pow 5305 ax-pr 5372 ax-un 7674 ax-inf2 9538 ax-cnex 11069 ax-resscn 11070 ax-1cn 11071 ax-icn 11072 ax-addcl 11073 ax-addrcl 11074 ax-mulcl 11075 ax-mulrcl 11076 ax-mulcom 11077 ax-addass 11078 ax-mulass 11079 ax-distr 11080 ax-i2m1 11081 ax-1ne0 11082 ax-1rid 11083 ax-rnegex 11084 ax-rrecex 11085 ax-cnre 11086 ax-pre-lttri 11087 ax-pre-lttrn 11088 ax-pre-ltadd 11089 ax-pre-mulgt0 11090 ax-pre-sup 11091 ax-addf 11092

This theorem depends on definitions: df-bi 207 df-an 396 df-or 848 df-3or 1087 df-3an 1088 df-tru 1544 df-fal 1554 df-ex 1781 df-nf 1785 df-sb 2068 df-mo 2537 df-eu 2566 df-clab 2712 df-cleq 2725 df-clel 2808 df-nfc 2882 df-ne 2930 df-nel 3034 df-ral 3049 df-rex 3058 df-rmo 3347 df-reu 3348 df-rab 3397 df-v 3439 df-sbc 3738 df-csb 3847 df-dif 3901 df-un 3903 df-in 3905 df-ss 3915 df-pss 3918 df-nul 4283 df-if 4475 df-pw 4551 df-sn 4576 df-pr 4578 df-tp 4580 df-op 4582 df-uni 4859 df-int 4898 df-iun 4943 df-iin 4944 df-br 5094 df-opab 5156 df-mpt 5175 df-tr 5201 df-id 5514 df-eprel 5519 df-po 5527 df-so 5528 df-fr 5572 df-se 5573 df-we 5574 df-xp 5625 df-rel 5626 df-cnv 5627 df-co 5628 df-dm 5629 df-rn 5630 df-res 5631 df-ima 5632 df-pred 6253 df-ord 6314 df-on 6315 df-lim 6316 df-suc 6317 df-iota 6442 df-fun 6488 df-fn 6489 df-f 6490 df-f1 6491 df-fo 6492 df-f1o 6493 df-fv 6494 df-isom 6495 df-riota 7309 df-ov 7355 df-oprab 7356 df-mpo 7357 df-of 7616 df-om 7803 df-1st 7927 df-2nd 7928 df-supp 8097 df-frecs 8217 df-wrecs 8248 df-recs 8297 df-rdg 8335 df-1o 8391 df-2o 8392 df-er 8628 df-map 8758 df-pm 8759 df-ixp 8828 df-en 8876 df-dom 8877 df-sdom 8878 df-fin 8879 df-fsupp 9253 df-fi 9302 df-sup 9333 df-inf 9334 df-oi 9403 df-card 9839 df-pnf 11155 df-mnf 11156 df-xr 11157 df-ltxr 11158 df-le 11159 df-sub 11353 df-neg 11354 df-div 11782 df-nn 12133 df-2 12195 df-3 12196 df-4 12197 df-5 12198 df-6 12199 df-7 12200 df-8 12201 df-9 12202 df-n0 12389 df-z 12476 df-dec 12595 df-uz 12739 df-q 12849 df-rp 12893 df-xneg 13013 df-xadd 13014 df-xmul 13015 df-ioo 13251 df-ioc 13252 df-ico 13253 df-icc 13254 df-fz 13410 df-fzo 13557 df-fl 13698 df-seq 13911 df-exp 13971 df-fac 14183 df-bc 14212 df-hash 14240 df-shft 14976 df-cj 15008 df-re 15009 df-im 15010 df-sqrt 15144 df-abs 15145 df-limsup 15380 df-clim 15397 df-rlim 15398 df-sum 15596 df-ef 15976 df-sin 15978 df-cos 15979 df-pi 15981 df-struct 17060 df-sets 17077 df-slot 17095 df-ndx 17107 df-base 17123 df-ress 17144 df-plusg 17176 df-mulr 17177 df-starv 17178 df-sca 17179 df-vsca 17180 df-ip 17181 df-tset 17182 df-ple 17183 df-ds 17185 df-unif 17186 df-hom 17187 df-cco 17188 df-rest 17328 df-topn 17329 df-0g 17347 df-gsum 17348 df-topgen 17349 df-pt 17350 df-prds 17353 df-xrs 17408 df-qtop 17413 df-imas 17414 df-xps 17416 df-mre 17490 df-mrc 17491 df-acs 17493 df-mgm 18550 df-sgrp 18629 df-mnd 18645 df-submnd 18694 df-mulg 18983 df-cntz 19231 df-cmn 19696 df-psmet 21285 df-xmet 21286 df-met 21287 df-bl 21288 df-mopn 21289 df-fbas 21290 df-fg 21291 df-cnfld 21294 df-top 22810 df-topon 22827 df-topsp 22849 df-bases 22862 df-cld 22935 df-ntr 22936 df-cls 22937 df-nei 23014 df-lp 23052 df-perf 23053 df-cn 23143 df-cnp 23144 df-haus 23231 df-tx 23478 df-hmeo 23671 df-fil 23762 df-fm 23854 df-flim 23855 df-flf 23856 df-xms 24236 df-ms 24237 df-tms 24238 df-cncf 24799 df-limc 25795 df-dv 25796

This theorem is referenced by: (None)

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