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hossam1122
 3 years ago
prove that sin54sin18=1/2
hossam1122
 3 years ago
prove that sin54sin18=1/2

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GoldRush18
 3 years ago
Best ResponseYou've already chosen the best response.00.809020.30902=0.5 or 1/2

GoldRush18
 3 years ago
Best ResponseYou've already chosen the best response.0or should i say 0.5=1/2

hossam1122
 3 years ago
Best ResponseYou've already chosen the best response.0@GoldRush18 u have to prove it using trigonometric functions and rules , not using calculator :D

hossam1122
 3 years ago
Best ResponseYou've already chosen the best response.0well i got cos36sin18 and dont know what to do , can u prove it with explanation pls :)

MelindaR
 3 years ago
Best ResponseYou've already chosen the best response.1Idk if this helps, but Sin(3theta)=3Sin(theta)4(Sin(theta))^3 I tried using it and I got  4 sin³ 18 + 2 sin 18  1/2 = 0

blockcolder
 3 years ago
Best ResponseYou've already chosen the best response.1Use this identity: \[\sin A\sin B=2 \cos{\frac{A+B}{2}}\sin{\frac{AB}{2}}\]

hossam1122
 3 years ago
Best ResponseYou've already chosen the best response.0thanks will do that :D @blockcolder

hossam1122
 3 years ago
Best ResponseYou've already chosen the best response.0thanks i got it now it should be like this 2cos(36)sin(18) and multiply by cos18/cos18 as it equals 1 so cos(36)sin(36)/cos(18) and then multiply by 2 and 1/2 so 1/2sin72/cos18 then use co function so sin72= cos18 1/2cos(18)/cos(18) cosines cancel each other so = 1/2
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