We will use the chain rule for differentiation. The chain rule states that if $y = f(g(x))$, then $\frac{dy}{dx} = f'(g(x)) \cdot g'(x)$.
In this case, let $u = 1 + \tan^{-1}x$. Then $y = u^3$.
First, find the derivative of $y$ with respect to
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