Use the Trigonometric Substitution U = a Tan $\theta$ , Where 0

Multiple Choice

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

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