(1)设函数$y=y(x)$由 $\begin{cases} x= \arctan t \\ y= \ln (1+t^{2}) \end{cases}$确定，求 $\dfrac {dy}{dx}$，$\dfrac {d^{2}y}{dx^{2}}$.
(2)设函数$y=y(x)$由 $\begin{cases} x=1+t^{2} \\ y= \sin 2t \end{cases} $确定，求 $\dfrac {dy}{dx}$, $\dfrac {d^{2}y}{dx^{2}}$.
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