Answer
$sec120^{\circ}$ = -2
Work Step by Step
Recall: $\sec\theta$ = $\frac{1}{\cos\theta}$
Substitute: $\sec120^{\circ}$ = $\frac{1}{\cos120^{\circ}}$
Simplify: $\sec120^{\circ}$ = $\frac{1}{\frac{-1}{2}}$
$\sec120^{\circ}$ = $\frac{1}{1}$ $\times$ $\frac{2}{-1}$
$\sec120^{\circ}$ = -2