Use the substitution x=3tan(θ)\displaystyle {x}={3}{\tan{{\left(\theta\right)}}} to evaluate the indefinite integral

99dxx2x2+9\displaystyle \int{\frac{{{99}{\left.{d}{x}\right.}}}{{{x}^{{2}}\sqrt{{{x}^{{2}}+{9}}}}}}


  +C\displaystyle +{C}