Find the exact value of each expression. Answers must be in radians. \text { 1) } \cos ^{-1} \frac{1}{2} \text { 2) } \tan ^{-1}(-\sqrt{3}) \text { 3) } \sin

^{-1}-\frac{\sqrt{3}}{2} \text { 4) } \tan ^{-1}-\frac{\sqrt{3}}{3} \text { 5) } \sin ^{-1} \frac{\sqrt{2}}{2} \text { 6) } \cos ^{-1}-\frac{\sqrt{2}}{2}