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Theorem coskpi 26487

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 12529	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → 𝐾 ∈ ℂ)
2		2cn 12256	. . . . . . . . . . 11 ⊢ 2 ∈ ℂ
3		picn 26422	. . . . . . . . . . 11 ⊢ π ∈ ℂ
4		mul12 11311	. . . . . . . . . . 11 ⊢ ((𝐾 ∈ ℂ ∧ 2 ∈ ℂ ∧ π ∈ ℂ) → (𝐾 · (2 · π)) = (2 · (𝐾 · π)))
5	2, 3, 4	mp3an23 1456	. . . . . . . . . 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 6844	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · (2 · π))) = (cos‘(2 · (𝐾 · π))))
8		cos2kpi 26448	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · (2 · π))) = 1)
9		zre 12528	. . . . . . . . . . 11 ⊢ (𝐾 ∈ ℤ → 𝐾 ∈ ℝ)
10		pire 26421	. . . . . . . . . . 11 ⊢ π ∈ ℝ
11		remulcl 11123	. . . . . . . . . . 11 ⊢ ((𝐾 ∈ ℝ ∧ π ∈ ℝ) → (𝐾 · π) ∈ ℝ)
12	9, 10, 11	sylancl 587	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → (𝐾 · π) ∈ ℝ)
13	12	recnd 11173	. . . . . . . . 9 ⊢ (𝐾 ∈ ℤ → (𝐾 · π) ∈ ℂ)
14		cos2t 16145	. . . . . . . . 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 2780	. . . . . . 7 ⊢ (𝐾 ∈ ℤ → ((2 · ((cos‘(𝐾 · π))↑2)) − 1) = 1)
17	12	recoscld 16111	. . . . . . . . . . 11 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · π)) ∈ ℝ)
18	17	recnd 11173	. . . . . . . . . 10 ⊢ (𝐾 ∈ ℤ → (cos‘(𝐾 · π)) ∈ ℂ)
19	18	sqcld 14106	. . . . . . . . 9 ⊢ (𝐾 ∈ ℤ → ((cos‘(𝐾 · π))↑2) ∈ ℂ)
20		mulcl 11122	. . . . . . . . 9 ⊢ ((2 ∈ ℂ ∧ ((cos‘(𝐾 · π))↑2) ∈ ℂ) → (2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ)
21	2, 19, 20	sylancr 588	. . . . . . . 8 ⊢ (𝐾 ∈ ℤ → (2 · ((cos‘(𝐾 · π))↑2)) ∈ ℂ)
22		ax-1cn 11096	. . . . . . . . 9 ⊢ 1 ∈ ℂ
23		subadd 11396	. . . . . . . . 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 1456	. . . . . . . 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 12339	. . . . . . 7 ⊢ (2 · 1) = 2
28		df-2 12244	. . . . . . 7 ⊢ 2 = (1 + 1)
29	27, 28	eqtr2i 2760	. . . . . 6 ⊢ (1 + 1) = (2 · 1)
30	26, 29	eqtr3di 2786	. . . . 5 ⊢ (𝐾 ∈ ℤ → (2 · ((cos‘(𝐾 · π))↑2)) = (2 · 1))
31		2cnne0 12386	. . . . . . 7 ⊢ (2 ∈ ℂ ∧ 2 ≠ 0)
32		mulcan 11787	. . . . . . 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 1456	. . . . . 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 14157	. . . 4 ⊢ (1↑2) = 1
37	35, 36	eqtr4di 2789	. . 3 ⊢ (𝐾 ∈ ℤ → ((cos‘(𝐾 · π))↑2) = (1↑2))
38		1re 11144	. . . 4 ⊢ 1 ∈ ℝ
39		sqabs 15269	. . . 4 ⊢ (((cos‘(𝐾 · π)) ∈ ℝ ∧ 1 ∈ ℝ) → (((cos‘(𝐾 · π))↑2) = (1↑2) ↔ (abs‘(cos‘(𝐾 · π))) = (abs‘1)))
40	17, 38, 39	sylancl 587	. . 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 15259	. 2 ⊢ (abs‘1) = 1
43	41, 42	eqtrdi 2787	1 ⊢ (𝐾 ∈ ℤ → (abs‘(cos‘(𝐾 · π))) = 1)

Colors of variables: wff setvar class

Syntax hints: → wi 4 ↔ wb 206 ∧ wa 395 = wceq 1542 ∈ wcel 2114 ≠ wne 2932 ‘cfv 6498 (class class class)co 7367 ℂcc 11036 ℝcr 11037 0cc0 11038 1c1 11039 + caddc 11041 · cmul 11043 − cmin 11377 2c2 12236 ℤcz 12524 ↑cexp 14023 abscabs 15196 cosccos 16029 πcpi 16031

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1797 ax-4 1811 ax-5 1912 ax-6 1969 ax-7 2010 ax-8 2116 ax-9 2124 ax-10 2147 ax-11 2163 ax-12 2185 ax-ext 2708 ax-rep 5212 ax-sep 5231 ax-nul 5241 ax-pow 5307 ax-pr 5375 ax-un 7689 ax-inf2 9562 ax-cnex 11094 ax-resscn 11095 ax-1cn 11096 ax-icn 11097 ax-addcl 11098 ax-addrcl 11099 ax-mulcl 11100 ax-mulrcl 11101 ax-mulcom 11102 ax-addass 11103 ax-mulass 11104 ax-distr 11105 ax-i2m1 11106 ax-1ne0 11107 ax-1rid 11108 ax-rnegex 11109 ax-rrecex 11110 ax-cnre 11111 ax-pre-lttri 11112 ax-pre-lttrn 11113 ax-pre-ltadd 11114 ax-pre-mulgt0 11115 ax-pre-sup 11116 ax-addf 11117

This theorem depends on definitions: df-bi 207 df-an 396 df-or 849 df-3or 1088 df-3an 1089 df-tru 1545 df-fal 1555 df-ex 1782 df-nf 1786 df-sb 2069 df-mo 2539 df-eu 2569 df-clab 2715 df-cleq 2728 df-clel 2811 df-nfc 2885 df-ne 2933 df-nel 3037 df-ral 3052 df-rex 3062 df-rmo 3342 df-reu 3343 df-rab 3390 df-v 3431 df-sbc 3729 df-csb 3838 df-dif 3892 df-un 3894 df-in 3896 df-ss 3906 df-pss 3909 df-nul 4274 df-if 4467 df-pw 4543 df-sn 4568 df-pr 4570 df-tp 4572 df-op 4574 df-uni 4851 df-int 4890 df-iun 4935 df-iin 4936 df-br 5086 df-opab 5148 df-mpt 5167 df-tr 5193 df-id 5526 df-eprel 5531 df-po 5539 df-so 5540 df-fr 5584 df-se 5585 df-we 5586 df-xp 5637 df-rel 5638 df-cnv 5639 df-co 5640 df-dm 5641 df-rn 5642 df-res 5643 df-ima 5644 df-pred 6265 df-ord 6326 df-on 6327 df-lim 6328 df-suc 6329 df-iota 6454 df-fun 6500 df-fn 6501 df-f 6502 df-f1 6503 df-fo 6504 df-f1o 6505 df-fv 6506 df-isom 6507 df-riota 7324 df-ov 7370 df-oprab 7371 df-mpo 7372 df-of 7631 df-om 7818 df-1st 7942 df-2nd 7943 df-supp 8111 df-frecs 8231 df-wrecs 8262 df-recs 8311 df-rdg 8349 df-1o 8405 df-2o 8406 df-er 8643 df-map 8775 df-pm 8776 df-ixp 8846 df-en 8894 df-dom 8895 df-sdom 8896 df-fin 8897 df-fsupp 9275 df-fi 9324 df-sup 9355 df-inf 9356 df-oi 9425 df-card 9863 df-pnf 11181 df-mnf 11182 df-xr 11183 df-ltxr 11184 df-le 11185 df-sub 11379 df-neg 11380 df-div 11808 df-nn 12175 df-2 12244 df-3 12245 df-4 12246 df-5 12247 df-6 12248 df-7 12249 df-8 12250 df-9 12251 df-n0 12438 df-z 12525 df-dec 12645 df-uz 12789 df-q 12899 df-rp 12943 df-xneg 13063 df-xadd 13064 df-xmul 13065 df-ioo 13302 df-ioc 13303 df-ico 13304 df-icc 13305 df-fz 13462 df-fzo 13609 df-fl 13751 df-seq 13964 df-exp 14024 df-fac 14236 df-bc 14265 df-hash 14293 df-shft 15029 df-cj 15061 df-re 15062 df-im 15063 df-sqrt 15197 df-abs 15198 df-limsup 15433 df-clim 15450 df-rlim 15451 df-sum 15649 df-ef 16032 df-sin 16034 df-cos 16035 df-pi 16037 df-struct 17117 df-sets 17134 df-slot 17152 df-ndx 17164 df-base 17180 df-ress 17201 df-plusg 17233 df-mulr 17234 df-starv 17235 df-sca 17236 df-vsca 17237 df-ip 17238 df-tset 17239 df-ple 17240 df-ds 17242 df-unif 17243 df-hom 17244 df-cco 17245 df-rest 17385 df-topn 17386 df-0g 17404 df-gsum 17405 df-topgen 17406 df-pt 17407 df-prds 17410 df-xrs 17466 df-qtop 17471 df-imas 17472 df-xps 17474 df-mre 17548 df-mrc 17549 df-acs 17551 df-mgm 18608 df-sgrp 18687 df-mnd 18703 df-submnd 18752 df-mulg 19044 df-cntz 19292 df-cmn 19757 df-psmet 21344 df-xmet 21345 df-met 21346 df-bl 21347 df-mopn 21348 df-fbas 21349 df-fg 21350 df-cnfld 21353 df-top 22859 df-topon 22876 df-topsp 22898 df-bases 22911 df-cld 22984 df-ntr 22985 df-cls 22986 df-nei 23063 df-lp 23101 df-perf 23102 df-cn 23192 df-cnp 23193 df-haus 23280 df-tx 23527 df-hmeo 23720 df-fil 23811 df-fm 23903 df-flim 23904 df-flf 23905 df-xms 24285 df-ms 24286 df-tms 24287 df-cncf 24845 df-limc 25833 df-dv 25834

This theorem is referenced by: (None)

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