Now, the limit becomes:
$\lim_{x \rightarrow \infty} 4x \tan^{-1}\frac{1}{x+1}$.
Now, let's make a substitution: let $u = x + 1$. Then, as $x \rightarrow \infty$, $u \rightarrow \infty$, and the limit becomes:
$\lim_{u \rightarrow \infty} 4(u - 1)
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