Answer
$\ln \left( x^{2}+1\right) +c$
Work Step by Step
$U=x^{2}+1\Rightarrow dU=2xdx$
$$\Rightarrow \int \dfrac {2x}{x^{2}+1}dx=\int \dfrac {dU}{U}=\ln U+c=\ln \left( x^{2}+1\right) +c$$
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