trigonometry - Solving $cos(x/2) = sin x$

Can anyone give me just a hint as to how to go about solving this? Yes it is for homework, but I don't want an answer, just a bit of guidance. I'm thinking the half angle formula for the first bit, but it doesn't seem to look right.

$$\cos(x/2)-\sin(x) = 0$$

Thanks!

Answer

Let $y=\frac{x}{2}$, so that your equation is
$$\cos(y)=\sin(2y).$$

Do you know any formulas that you can use here?