Chapter 7 - Trigonometry and Periodic Functions - 7.3 Radians and Arc Length - Exercises and Problems for Section 7.3 - Exercises and Problems - Page 284: 5

$\frac{5\pi}{6}$ rad.

Use the conversion $360^\circ=2\pi \, \textrm{rad.}$ to simplify the expression to $$150^\circ \cdot \frac{2\pi \, \textrm{rad.}}{360^\circ}=\frac{150\pi}{180} \, \textrm{rad.}=\frac{5\pi}{6} \, \textrm{rad.}$$