The sum of solutions of the equation

Question:

The sum of solutions of the equation $\frac{\cos x}{1+\sin x}=|\tan 2 x|, x \in\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)-\left\{\frac{\pi}{4},-\frac{\pi}{4}\right\}$ is : 

  1. (1) $-\frac{11 \pi}{30}$

  2. $\frac{\pi}{10}$

  3. $-\frac{7 \pi}{30}$

  4. $-\frac{\pi}{15}$


Correct Option: 1,

Solution:

$\frac{\cos x}{1+\sin x}=|\tan 2 x|$

$\Rightarrow \frac{\cos ^{2} x / 2-\sin ^{2} x / 2}{(\cos x / 2+\sin x / 2}=1 \tan 2 x$

$\Rightarrow \tan ^{2}\left(\frac{\pi}{4}-\frac{x}{2}\right)=\tan ^{2} 2 x$

$\Rightarrow 2 \mathrm{x}=\mathrm{n} \pi \pm\left(\frac{\pi}{4}-\frac{\mathrm{X}}{2}\right)$

$\Rightarrow x=\frac{-3 \pi}{10}, \frac{-\pi}{6}, \frac{\pi}{10}$

or sum $=\frac{-11 \pi}{6}$.

 

 

 

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