Let $x = 2 \tan \theta$ $0 \leq \theta < \frac { \pi } { 2 }$

Essay

Let $x = 2 \tan \theta$
, $0 \leq \theta < \frac { \pi } { 2 }$
. Simplify the expression. $\frac { 1 } { x ^ { 2 } \sqrt { 4 + x ^ { 2 } } }$