Trigonometry - Inverse Trigonometric Functions

Giving your answer in radians as a multiple of \(\pi\), state the principal value of

1. \(\cos^{-1} \left( \frac{\sqrt{3}}{2} \right)\).
2. \(\sin^{-1} \left( -\frac{1}{2} \right)\).

Use the results of part (a) and (b) to find the exact value of \(\cos^{-1} \left( \frac{\sqrt{3}}{2} \right) - 2\sin^{-1} \left( -\frac{1}{2} \right)\).