If $y=\tan ^{-1}\left[\frac{1}{1+x+x^2}\right]+\tan ^{-1}\left[\frac{1}{x^2+3 x+3}\right], x>0$, then…

If $y=\tan ^{-1}\left[\frac{1}{1+x+x^2}\right]+\tan ^{-1}\left[\frac{1}{x^2+3 x+3}\right], x>0$, then $\frac{d y}{d x}=$
  1. $\frac{1}{1+x^2}-\frac{1}{1+(x+2)^2}$
  2. $\frac{-1}{1+x^2}+\frac{1}{1+(x+2)^2}$
  3. $\frac{1}{1+x^2}+\frac{1}{1+(x+2)^2}$
  4. $\frac{-1}{1+\mathrm{x}^2}-\frac{1}{1+(\mathrm{x}+2)^2}$

Solution

$\begin{aligned} & y=\tan ^{-1}\left[\frac{1}{1+x+x^2}\right]+\tan ^{-1}\left[\frac{1}{x^2+3 x+3}\right] \\ & =\tan ^{-1}\left[\frac{1}{1+x(1+x)}\right]+\tan ^{-1}\left[\frac{1}{1+(x+2)(x+1)}\right] \\ & =\tan ^{-1}\left[\frac{(x+1)-1}{1+(x+1) x)}\right]+\tan ^{-1}\left[\frac{(x+2)-(x+1)}{1+(x+2)(x+1)}\right] \\ & =\tan ^{-1}(\mathrm{x}+1)-\tan ^{-1}(\mathrm{x}+2)-\tan ^{-1}(\mathrm{x}+1) \\ & =\tan ^{-1}(\mathrm{x}+2)-\tan ^{-1}(\mathrm{x}) \\ & \therefore \frac{\mathrm{dy}}{\mathrm{dx}}=\frac{1}{1+(\mathrm{x}+2)^2}-\frac{1}{1+\mathrm{x}^2} \\ & \end{aligned}$

Asked in: MHT CET 2021 (21 Sep Shift 2)

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