# How do you test the improper integral int (2x)/(sqrt(x^2+1)) dx from (-oo, oo) and evaluate if possible?

$\frac{2 x}{\sqrt{{x}^{2} + 1}}$ is an odd function so
${\int}_{- a}^{a} \frac{2 x}{\sqrt{{x}^{2} + 1}} \mathrm{dx} = 0$