How do you find the exact value of sec^-1(2)?

${60}^{\circ} , {300}^{\circ}$
${\sec}^{-} 1 \left(2\right) - \to a r c \sec \left(2\right)$
If sec = 2 --> $\cos x = \frac{1}{2}$
$\cos x = \frac{1}{2}$ --> arc $x = \frac{\pi}{3}$, or 60^@
Trig unit circle gives another arc x that has the same cos value (1/2): $x = - \frac{\pi}{3} \mathmr{and} {300}^{\circ}$