If $x = 8 \cos \theta$ , Use Trigonometric Substitution to Write

Multiple Choice

If $x = 8 \cos \theta$ , use trigonometric substitution to write $\sqrt { 64 - x ^ { 2 } }$ as a trigonometric function of $\theta$ , where $0 < \theta < \pi$ .

A) $8 \sec \theta$
B) $8 \sin \theta$
C) $8 \cot \theta$
D) $8 \cos \theta$
E) $8 \csc \theta$