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

a. cos x - 4 cos x sin2x
b. -sin3x + 2 sin x cos x
c. -sin2x + 2 sin x cos x
d. 2 sin2x cos x - 2 sin x cos x

Option A

Solution:

Given that we have to rewrite with only sin x and cos x

Given is cos 3x

We know that,

Therefore,

 ---- eqn 1

We know that,

Substituting these values in eqn 1

 -------- eqn 2

We know that,

Applying this in above eqn 2, we get

Therefore,

Option A is correct

step-by-step explanation: