Use the Trigonometric Substitution $x = 8 \sec ( \theta )$

Multiple Choice

Use the trigonometric substitution $x = 8 \sec ( \theta )$ to write the expression $\sqrt { x ^ { 2 } - 64 }$ as a trigonometric function of $\theta$ , where $0 < \theta < \frac { \pi } { 2 }$ .

A) $8 \tan ( \theta )$
B) $64 \tan ( \theta )$
C) $64 \sec ( \theta )$
D) $8 \sec ( \theta )$
E) $8 \sec ( \theta ) - 1$