1. anonymous

cos^2x = 1-sin^2x. So, substitute and see what you get.

2. Mertsj

$\cos ^{2}x+\cos ^{3}xsinx=\frac{1}{2}$

3. Mertsj

Is that the equation?

4. Mertsj

Or is it $\cos2x+\cos3xsinx=\frac{1}{2}$

5. anonymous

Your version may be the right one as I can't see how the "former one" I interpreted could hold true.