# Math Help - Prove the identity

1. ## Prove the identity

This is another problem which I am not able to complete

Prove the following identity.

sin(4x) = 8sin(x)cos^3(x)-4sin(x)cos(x)

2. ## Re: Prove the identity

Originally Posted by MathRaven
This is another problem which I am not able to complete
Prove the following identity.
sin(4x) = 8sin(x)cos^3(x)-4sin(x)cos(x)
$\sin(4x)=2\sin(2x)\cos(2x)=2[2\sin(x)\cos(x)][2\cos^2(x)-1]$

3. ## Re: Prove the identity

is that showing all the steps which you took?

4. ## Re: Prove the identity

Originally Posted by MathRaven
is that showing all the steps which you took?
it's your turn, how did he get from the 1st to the 2nd step? ... and from the 2nd to the 3rd?