With usual notations in $\Delta \mathrm{ABC}$, if $C=90^{\circ}$, then $\tan…

With usual notations in $\Delta \mathrm{ABC}$, if $C=90^{\circ}$, then $\tan ^{-1}\left(\frac{a}{b+c}\right)+\tan ^{-1}\left(\frac{b}{c+a}\right)=$
  1. $\frac{\pi}{4}$
  2. $\frac{\pi}{6}$
  3. $\pi$
  4. $\frac{\pi}{3}$

Solution

$\therefore \quad \tan ^{-1}\left(\frac{a}{b+c}\right)+\tan ^{-1}\left(\frac{b}{c+a}\right)$ $=\tan ^{-1}\left[\frac{\frac{a}{b+c}+\frac{b}{c+a}}{1-\left(\frac{a}{b+c}\right)\left(\frac{b}{c+a}\right)}\right]$ $=\tan ^{-1}\left[\frac{a c+a^{2}+b c+b^{2}}{a c+b c+a b+c^{2}-a b}\right]=\tan ^{-1}\left(\frac{a c+b c+c^{2}}{a c+b c+c^{2}}\right) \quad \ldots\left[\because a^{2}+b^{2}=c^{2}\right.$, refer diagram $]$ $=\tan ^{-1}(1)=\frac{\pi}{4}$

Asked in: MHT CET 2020 (14 Oct Shift 1)

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