If X = 3 Cot θ,Use Trigonometric Substitution to Write $\sqrt { 9 + x ^ { 2 } }$

Multiple Choice

If x = 3 cot θ,use trigonometric substitution to write $\sqrt { 9 + x ^ { 2 } }$ as a trigonometric function of θ,where $0 < \theta < \pi$ . ​

A) ​3 sec θ
B) ​3 csc θ
C) ​3 cos θ
D) ​3 sin θ
E) ​3 cot θ