trigonometry - Express $sin 3theta$ and $cos 3theta$ as functions of $sin theta$ and $cos theta$ using Euler's identity

Using Euler's identity ($e^{in\theta}=\cos n\theta+i \sin n\theta$), express $\sin 3\theta$ and $\cos 3\theta$ as functions of $\sin \theta$ and $\cos \theta$.

Any ideas?