2. Are you sure you're not trying to find $\displaystyle \sin{\frac{\pi}{12}}$ or $\displaystyle \cos{\frac{\pi}{12}}$?
4. Either evaluate $\displaystyle \cos{\left(\frac{\pi}{3} - \frac{\pi}{4}\right)}$ using the angle difference identity, or evaluate $\displaystyle \cos{\left(\frac{1}{2}\cdot \frac{\pi}{6}\right)}$ using the half angle identity.