Answer
$$\frac{{5\pi }}{6}{\text{radians}}$$
Work Step by Step
$$\eqalign{
& {\text{we know that }}{{\text{1}}^ \circ } = \frac{\pi }{{180}}{\text{radians}}{\text{. Thus}}{\text{,}} \cr
& {150^ \circ } = 150\left( {\frac{\pi }{{180}}} \right){\text{radians}} \cr
& {\text{multiplying}} \cr
& {150^ \circ } = \frac{{150\pi }}{{180}}{\text{radians}} \cr
& {150^ \circ } = \frac{{5\pi }}{6}{\text{radians}} \cr} $$