Evaluate each expression. Give exact values.  

1. $\tan\left(\frac{2\pi}{3}\right)$ 

   Unit circle (a):

   

2. $\sin\left(\frac{5\pi}{4}\right)$ 

   Unit circle (b):

   

3. $\cos\left(\frac{11\pi}{6}\right)$ 

   Unit circle (c):

   

4. $\tan\left(\frac{4\pi}{3}\right)$ 

   Unit circle (d):