The derivative of $\cot ^{-1} x$ w.r.t $\log \left(1+x^{2}\right)$ is

The derivative of $\cot ^{-1} x$ w.r.t $\log \left(1+x^{2}\right)$ is
  1. $-2 x$
  2. $-\frac{1}{2 x}$
  3. $\frac{1}{2 x}$
  4. $2 x$

Solution

Let $u=\cot ^{-1} x$ and $v=\log \left(1+x^{2}\right)$ $\begin{array}{l}\frac{d u}{d x}=\frac{-1}{1+x^{2}} \text { and } \frac{d v}{d x}=\frac{2 x}{1+x^{2}} \\ \therefore \frac{d u}{d v}=\frac{\left(\frac{d u}{d x}\right)}{\left(\frac{d v}{d x}\right)}=\frac{\left(\frac{-1}{1+x^{2}}\right)}{\left(\frac{2 x}{1+x^{2}}\right)}=\frac{-1}{2 x}\end{array}$

Asked in: MHT CET 2020 (19 Oct Shift 1)

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