# Prove the identity

• July 8th 2012, 01:14 PM
MathRaven
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)
• July 8th 2012, 01:28 PM
Plato
Re: Prove the identity
Quote:

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)

$\sin(4x)=2\sin(2x)\cos(2x)=2[2\sin(x)\cos(x)][2\cos^2(x)-1]$
• July 8th 2012, 01:38 PM
MathRaven
Re: Prove the identity
is that showing all the steps which you took?
• July 8th 2012, 01:42 PM
skeeter
Re: Prove the identity
Quote:

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?