Find the Integral Using an Appropriate Trigonometric Substitution $$\int \frac { 1 } { x ^ { 2 } \sqrt { x ^ { 2 } + 36 } } d x$$

Find the integral using an appropriate trigonometric substitution.
$$\int \frac { 1 } { x ^ { 2 } \sqrt { x ^ { 2 } + 36 } } d x$$