Question

Rewrite with only sin x and cos x.
cos 3x

Answer 1

\[\cos 3x=\cos \left( 2x+x \right)=?\]
cos(a+b)=cos a cos b-sin a sin b

Answer 2

sin 2a =2sin a cos a

Answer 3

I'm sorry, I'm lost

Answer 4

you want to write formula for cos 3x or you want to derive the formula.

Answer 5

The question asks to rewrite cos 3x

Answer 6

\[\cos 3x=4\cos ^{3}x-3\cos x\]
if you want to derive this formula then proceed as written above.

Answer 7

@jdoe0001