For the Simple Harmonic Motion Described by the Trigonometric Function $d = 9 \cos \frac { 6 \pi } { 5 } t$

Multiple Choice

For the simple harmonic motion described by the trigonometric function, find the frequency.
$d = 9 \cos \frac { 6 \pi } { 5 } t$

A) $\frac { 3 } { 5 }$
B) $\frac { 6 \pi } { 5 }$
C) $\frac { 5 } { 3 }$
D) $\frac { 5 \pi } { 6 }$
E) $\frac { 5 } { 6 }$