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Let M and m respectively be the maximum and minimum values of the function f(x)=\tan ^{-1}(\sin x+\cos x)$ in $\left[0, \frac{\pi}{2}\right]. Then the value of \tan (\mathrm{M}-\mathrm{m}) is equal to:
Option: 1 2+\sqrt{3}
Option: 2 2-\sqrt{3}
Option: 3 3-2 \sqrt{2}
Option: 4 3+2 \sqrt{2}

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For  x\in \left [ 0,\pi/2 \right ],\\ 

\sin x +\cos x \in \left [ 1,\sqrt{2} \right ] \\

\Rightarrow \tan^{-1}\left ( \sin x+\cos x \right )\in\left [ \tan^{-1}1,\tan^{-1}\sqrt{2} \right ]\\

\Rightarrow M= \tan^{-1}\sqrt{2}\:\: \: \: m= \tan^{-1}= \frac{\pi}{4}\\

M-m= \tan^{-1}\sqrt{2}-\tan^{-1}1= \tan^{-1}\sqrt{2}-\frac{\pi}{4}\\

\tan\left ( M-m \right )= \tan\left ( \tan^{-1}\sqrt{2}-\frac{\pi}{4} \right )= \frac{\sqrt{2}-1}{1+\sqrt{2}}\\

                                                                       = \frac{\left ( \sqrt{2}-1 \right )^{2}}{2-1}

                                                                       = 3-2\sqrt{2}\\

Posted by

Kuldeep Maurya

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