# Euler's formula proof help

1. Feb 7, 2006

### mathhelp123

Hi. I am trying to prove that (2sin^4x(2cos^2x+1))/3 = [sin^2(2x)/6-1/3][cos(2x)].

I tried fixing the right side, changing cos2x to 1 - 2sin^2x, and I went all the way to

(4sin^2x-4sin^4x-2-8sin^4x+8sin^6x+4sin^2x)/6.

$$e^{4 i \theta} = \left( e^{i \theta} \right)^4$$