Find Angle -20° in Radian Measure as a Multiple Of \pi

Multiple Choice

Find angle -20° in radian measure as a multiple of $\pi$ .

A) 9 $\pi$
B) $\frac { \pi \sqrt { 2 } } { 2 }$
C) $- \frac { \pi } { 9 }$
D) $\frac { \pi \sqrt { 3 } } { 3 }$
E) $\frac { \pi } { 9 }$