- Thread starter
- #1

#### karush

##### Well-known member

- Jan 31, 2012

- 3,069

$$\sin(4x)$$

use $\sin2a=2\sin a\cos a$ then

$$\sin4x=2\sin 2x\cos 2x$$

with $\cos(2x) = \cos^2(x)-\sin^2(x)$ replace again

$$\sin 4x=4\sin x\cos x+\cos^2(x)-sin^2(x)$$

ok not real sure if this is what they are asking for

and if I should go further with it even if the steps are ok