If you replace (cos(x))^2 by 1 - (sin(x))^2, you will get a quadratic equation on sin(x).
I have to determine the angle that satisfies the following equation:
cos(x)=-2tan(x)
All I have managed to do is reexpress this as:
(cos(x))^2 + 2sin(x) = 0
However, I don't think this helps me? I am quite stuck with this problem and am not sure how to approach it. A worked solution would be greatly appreciated.