The Function $y = - 2 \cos \left( \frac { t } { 3 } \right)$

Multiple Choice

The function $y = - 2 \cos \left( \frac { t } { 3 } \right)$ models the displacement of an object moving in simple harmonic motion, where y is measured in inches and t in seconds. Find frequency of motion

A) $\frac { 1 } { 3 \pi }$

B) $\frac { 1 } { 6 \pi }$

C) $6 \pi$
D) $3 \pi$
E) $2 \pi$