Use the Trigonometric Substitution U = a Sin $\theta$ , Where -

Multiple Choice

Use the trigonometric substitution u = a sin $\theta$ , where - $\pi$ /2 < $\theta$ < $\pi$ /2 and a > 0 to simplify the expression $\sqrt { a ^ { 2 } - u ^ { 2 } }$ .

A) a csc $\theta$
B) a sin $\theta$
C) a tan $\theta$
D) a cos $\theta$
E) - a cos $\theta$