Use the Trigonometric Substitution U = a Tan θ,Where 0 $\sqrt { a ^ { 2 } + u ^ { 2 } }$

Multiple Choice

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

A) ​- a sec θ
B) ​a sec θ
C) ​a tan θ
D) ​a sin θ
E) ​a csc θ