Question

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

Answers: cos x - 4 cos x sin^2x
-sin^3x + 2 sin x cos x
-sin^2x + 2 sin x cos x
2 sin^2x cos x - 2 sin x cos x

Answer 1

try using the identity
cos(A+B)=cos(A)cos(B)-sin(A)sin(B)
sin(A+B)=sin(A)cos(B)+cos(A)sin(B)
You may need to go in two steps: cos(2x+x)=...
and substitute cos(2x)=cos(x+x)=...
and sin(2x)=sin(x+x)=...