Prove the identity

**MathRaven** · July 8th 2012, 01:14 PM

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)

**Plato** · July 8th 2012, 01:28 PM

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)

$\sin(4x)=2\sin(2x)\cos(2x)=2[2\sin(x)\cos(x)][2\cos^2(x)-1]$

**MathRaven** · July 8th 2012, 01:38 PM

is that showing all the steps which you took?

**skeeter** · July 8th 2012, 01:42 PM

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?

Thread: Prove the identity