Use the Trigonometric Substitution to Rewrite the Algebraic Expression as a Trigonometric

Multiple Choice

Use the trigonometric substitution to rewrite the algebraic expression as a trigonometric function of $\theta$ , where $0 < \theta < \frac { \pi } { 2 }$ . $\sqrt { 36 - 9 x ^ { 2 } } , x = 2 \cos \theta$

A) 2 cos $\theta$
B) 36 sin $\theta$
C) - 2 sin $\theta$
D) 36 cos $\theta$
E) 6 sin $\theta$