So there is this question which consists of 2 parts.

$$
a) \text{ Simplify } \frac{\sin2x}{1+\cos2x} \\
b) \text{ Hence, find the exact value of tan 15.}
$$

So far I've discovered that $ \text{a)} \tan x $
But I have no idea how to begin on part $b$, although I'm guessing the answer's correlated with a specific part of the working for part $a$. Can someone help me? Thanks in advance!