The Length Of $r = 6 \cos \theta$ With $x \in \left[ 0 , \frac { \pi } { 2 } \right]$

Multiple Choice

The length of $r = 6 \cos \theta$ with $x \in \left[ 0 , \frac { \pi } { 2 } \right]$ is

A) $9 \pi$
B) $6 \pi$
C) $3 \pi$
D) $\frac { 3 \pi } { 2 }$
E) $\frac { 3 \pi } { 5 }$