Question

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

Answer 1

sin 3x - cos x
= sin(2x+x) -cos x
Use sin(a+b) = sina cosb + sinb cosa
= sin(2x)cos(x) + cos(2x)sin(x) - cosx

sin(2x) = 2sin(x)cos(x)
cos(2x) = 1-2(sinx)^2

Sub. these two identities into sin(2x)cos(x) + cos(2x)sin(x) - cosx
Let see what you get..

Answer 2

2 sin x cos2x + sin x - 2 sin3x - cos x
right?

Answer 3

Yes.

Answer 4

Really? Thanks!

Answer 5

Really :)