Question

does cos3x will be equal to 4cosx*cos(60-x)*cos(60+x) ?

Answer 1

sin 2x = cos 3x

Answer 2

yes...

Answer 3

can u derive it?

Answer 4

hi this is the same guy: @apes...yes you can....I'll show you

Answer 5

LHS
Cos3x = 4Cos^3x - 3cosx

RHS
4cosx*cos(x-60)*cos(x+60)
= 4cosx*(cosxcos60 + sinxSin60)(cosxcos60 - sinxsin60)
= 4cosx(cos^2x*Cos^2(60) - sin^2x*Sin^2(60))
=4cosx(cos^2x*(1/4) - Sin^2x(3/4))
= cosx (cos^2x - 3sin^2x)
= cosx (cos^2x - 3(1-Cos^2x))
= cosx (cos^2x - 3 + 3cos^2x)
= cosx (4cos^2x - 3)
= 4cos^3x - 3 cosx

Answer 6

thankyou for your reply

Answer 7

no prob

Answer 8

not to be rude...can you mark my answer "best response" ps welcome to openstudy

Answer 9

Medal from me :), nice work buddy.