Answer
$\frac{2x}{1+x^2}$
Work Step by Step
Let $tan^{-1}x=y$, we have $tan(y)=x, sin(y)=\frac{x}{\sqrt {1+x^2}},cos(y)=\frac{1}{\sqrt {1+x^2}}$
Thus $sin(2tan^{-1}x)=sin(2y)=2sin(y)cos(y)=\frac{2x}{1+x^2}$
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