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

Multiple Choice

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

A) a tan θ
B) - a cot θ
C) a csc θ
D) a cos θ
E) a cot θ