Hello,
How do you solve for x? do you have to factor out cosine? how?
$\displaystyle -2cos(x)-2cos2(x) = 0$
Thanks!
$\displaystyle -2 \cos x -2 \cos(2x) = -2 \cos x - 2 (2 \cos^2x - 1) = -4 \cos^2 x - 2 \cos x + 2$ (this identity comes from your other post).
Hence
$\displaystyle -4 \cos^2 x - 2 \cos x + 2 = 0$
$\displaystyle 2 \cos^2 x + \cos x - 1 = 0$
Set $\displaystyle z = \cos x$, then
$\displaystyle 2z^2 + z - 1$.
Solve for z using the quadratic formula