Answer
$ \frac{1}{2}(\tan ^{-1} t)^2+c.$
Work Step by Step
We have
$$
\int \frac{\tan ^{-1} t d t}{1+t^{2}}=\int \tan ^{-1} t \ d (\tan ^{-1} t)\\
= \frac{1}{2}(\tan ^{-1} t)^2+c.
$$
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