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Mirrors > Home > MPE Home > Th. List > cosmul | Structured version Visualization version GIF version |
Description: Product of cosines can be rewritten as half the sum of certain cosines. This follows from cosadd 16149 and cossub 16153. (Contributed by David A. Wheeler, 26-May-2015.) |
Ref | Expression |
---|---|
cosmul | β’ ((π΄ β β β§ π΅ β β) β ((cosβπ΄) Β· (cosβπ΅)) = (((cosβ(π΄ β π΅)) + (cosβ(π΄ + π΅))) / 2)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | coscl 16111 | . . . . 5 β’ (π΄ β β β (cosβπ΄) β β) | |
2 | coscl 16111 | . . . . 5 β’ (π΅ β β β (cosβπ΅) β β) | |
3 | mulcl 11230 | . . . . 5 β’ (((cosβπ΄) β β β§ (cosβπ΅) β β) β ((cosβπ΄) Β· (cosβπ΅)) β β) | |
4 | 1, 2, 3 | syl2an 594 | . . . 4 β’ ((π΄ β β β§ π΅ β β) β ((cosβπ΄) Β· (cosβπ΅)) β β) |
5 | 2cnne0 12460 | . . . 4 β’ (2 β β β§ 2 β 0) | |
6 | 3anass 1092 | . . . 4 β’ ((((cosβπ΄) Β· (cosβπ΅)) β β β§ 2 β β β§ 2 β 0) β (((cosβπ΄) Β· (cosβπ΅)) β β β§ (2 β β β§ 2 β 0))) | |
7 | 4, 5, 6 | sylanblrc 588 | . . 3 β’ ((π΄ β β β§ π΅ β β) β (((cosβπ΄) Β· (cosβπ΅)) β β β§ 2 β β β§ 2 β 0)) |
8 | divcan3 11936 | . . 3 β’ ((((cosβπ΄) Β· (cosβπ΅)) β β β§ 2 β β β§ 2 β 0) β ((2 Β· ((cosβπ΄) Β· (cosβπ΅))) / 2) = ((cosβπ΄) Β· (cosβπ΅))) | |
9 | 7, 8 | syl 17 | . 2 β’ ((π΄ β β β§ π΅ β β) β ((2 Β· ((cosβπ΄) Β· (cosβπ΅))) / 2) = ((cosβπ΄) Β· (cosβπ΅))) |
10 | sincl 16110 | . . . . . 6 β’ (π΄ β β β (sinβπ΄) β β) | |
11 | sincl 16110 | . . . . . 6 β’ (π΅ β β β (sinβπ΅) β β) | |
12 | mulcl 11230 | . . . . . 6 β’ (((sinβπ΄) β β β§ (sinβπ΅) β β) β ((sinβπ΄) Β· (sinβπ΅)) β β) | |
13 | 10, 11, 12 | syl2an 594 | . . . . 5 β’ ((π΄ β β β§ π΅ β β) β ((sinβπ΄) Β· (sinβπ΅)) β β) |
14 | 4, 13, 4 | ppncand 11649 | . . . 4 β’ ((π΄ β β β§ π΅ β β) β ((((cosβπ΄) Β· (cosβπ΅)) + ((sinβπ΄) Β· (sinβπ΅))) + (((cosβπ΄) Β· (cosβπ΅)) β ((sinβπ΄) Β· (sinβπ΅)))) = (((cosβπ΄) Β· (cosβπ΅)) + ((cosβπ΄) Β· (cosβπ΅)))) |
15 | cossub 16153 | . . . . 5 β’ ((π΄ β β β§ π΅ β β) β (cosβ(π΄ β π΅)) = (((cosβπ΄) Β· (cosβπ΅)) + ((sinβπ΄) Β· (sinβπ΅)))) | |
16 | cosadd 16149 | . . . . 5 β’ ((π΄ β β β§ π΅ β β) β (cosβ(π΄ + π΅)) = (((cosβπ΄) Β· (cosβπ΅)) β ((sinβπ΄) Β· (sinβπ΅)))) | |
17 | 15, 16 | oveq12d 7444 | . . . 4 β’ ((π΄ β β β§ π΅ β β) β ((cosβ(π΄ β π΅)) + (cosβ(π΄ + π΅))) = ((((cosβπ΄) Β· (cosβπ΅)) + ((sinβπ΄) Β· (sinβπ΅))) + (((cosβπ΄) Β· (cosβπ΅)) β ((sinβπ΄) Β· (sinβπ΅))))) |
18 | 4 | 2timesd 12493 | . . . 4 β’ ((π΄ β β β§ π΅ β β) β (2 Β· ((cosβπ΄) Β· (cosβπ΅))) = (((cosβπ΄) Β· (cosβπ΅)) + ((cosβπ΄) Β· (cosβπ΅)))) |
19 | 14, 17, 18 | 3eqtr4rd 2779 | . . 3 β’ ((π΄ β β β§ π΅ β β) β (2 Β· ((cosβπ΄) Β· (cosβπ΅))) = ((cosβ(π΄ β π΅)) + (cosβ(π΄ + π΅)))) |
20 | 19 | oveq1d 7441 | . 2 β’ ((π΄ β β β§ π΅ β β) β ((2 Β· ((cosβπ΄) Β· (cosβπ΅))) / 2) = (((cosβ(π΄ β π΅)) + (cosβ(π΄ + π΅))) / 2)) |
21 | 9, 20 | eqtr3d 2770 | 1 β’ ((π΄ β β β§ π΅ β β) β ((cosβπ΄) Β· (cosβπ΅)) = (((cosβ(π΄ β π΅)) + (cosβ(π΄ + π΅))) / 2)) |
Colors of variables: wff setvar class |
Syntax hints: β wi 4 β§ wa 394 β§ w3a 1084 = wceq 1533 β wcel 2098 β wne 2937 βcfv 6553 (class class class)co 7426 βcc 11144 0cc0 11146 + caddc 11149 Β· cmul 11151 β cmin 11482 / cdiv 11909 2c2 12305 sincsin 16047 cosccos 16048 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1789 ax-4 1803 ax-5 1905 ax-6 1963 ax-7 2003 ax-8 2100 ax-9 2108 ax-10 2129 ax-11 2146 ax-12 2166 ax-ext 2699 ax-rep 5289 ax-sep 5303 ax-nul 5310 ax-pow 5369 ax-pr 5433 ax-un 7746 ax-inf2 9672 ax-cnex 11202 ax-resscn 11203 ax-1cn 11204 ax-icn 11205 ax-addcl 11206 ax-addrcl 11207 ax-mulcl 11208 ax-mulrcl 11209 ax-mulcom 11210 ax-addass 11211 ax-mulass 11212 ax-distr 11213 ax-i2m1 11214 ax-1ne0 11215 ax-1rid 11216 ax-rnegex 11217 ax-rrecex 11218 ax-cnre 11219 ax-pre-lttri 11220 ax-pre-lttrn 11221 ax-pre-ltadd 11222 ax-pre-mulgt0 11223 ax-pre-sup 11224 |
This theorem depends on definitions: df-bi 206 df-an 395 df-or 846 df-3or 1085 df-3an 1086 df-tru 1536 df-fal 1546 df-ex 1774 df-nf 1778 df-sb 2060 df-mo 2529 df-eu 2558 df-clab 2706 df-cleq 2720 df-clel 2806 df-nfc 2881 df-ne 2938 df-nel 3044 df-ral 3059 df-rex 3068 df-rmo 3374 df-reu 3375 df-rab 3431 df-v 3475 df-sbc 3779 df-csb 3895 df-dif 3952 df-un 3954 df-in 3956 df-ss 3966 df-pss 3968 df-nul 4327 df-if 4533 df-pw 4608 df-sn 4633 df-pr 4635 df-op 4639 df-uni 4913 df-int 4954 df-iun 5002 df-br 5153 df-opab 5215 df-mpt 5236 df-tr 5270 df-id 5580 df-eprel 5586 df-po 5594 df-so 5595 df-fr 5637 df-se 5638 df-we 5639 df-xp 5688 df-rel 5689 df-cnv 5690 df-co 5691 df-dm 5692 df-rn 5693 df-res 5694 df-ima 5695 df-pred 6310 df-ord 6377 df-on 6378 df-lim 6379 df-suc 6380 df-iota 6505 df-fun 6555 df-fn 6556 df-f 6557 df-f1 6558 df-fo 6559 df-f1o 6560 df-fv 6561 df-isom 6562 df-riota 7382 df-ov 7429 df-oprab 7430 df-mpo 7431 df-om 7877 df-1st 7999 df-2nd 8000 df-frecs 8293 df-wrecs 8324 df-recs 8398 df-rdg 8437 df-1o 8493 df-er 8731 df-pm 8854 df-en 8971 df-dom 8972 df-sdom 8973 df-fin 8974 df-sup 9473 df-inf 9474 df-oi 9541 df-card 9970 df-pnf 11288 df-mnf 11289 df-xr 11290 df-ltxr 11291 df-le 11292 df-sub 11484 df-neg 11485 df-div 11910 df-nn 12251 df-2 12313 df-3 12314 df-n0 12511 df-z 12597 df-uz 12861 df-rp 13015 df-ico 13370 df-fz 13525 df-fzo 13668 df-fl 13797 df-seq 14007 df-exp 14067 df-fac 14273 df-bc 14302 df-hash 14330 df-shft 15054 df-cj 15086 df-re 15087 df-im 15088 df-sqrt 15222 df-abs 15223 df-limsup 15455 df-clim 15472 df-rlim 15473 df-sum 15673 df-ef 16051 df-sin 16053 df-cos 16054 |
This theorem is referenced by: (None) |
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