Question
$\frac{{\cos A}}{{1 - \sin A}} = $
$ = \frac{{{{\left( {\cos \frac{A}{2} + \sin \frac{A}{2}} \right)}^2}}}{{\left( {\cos \frac{A}{2} + \sin \frac{A}{2}} \right)\,\left( {\cos \frac{A}{2} - \sin \frac{A}{2}} \right)}} $
$= \frac{{\cos \frac{A}{2} + \sin \frac{A}{2}}}{{\cos \frac{A}{2} - \sin \frac{A}{2}}}$
$ = \frac{{1 + \tan \frac{A}{2}}}{{1 - \tan \frac{A}{2}}}$, (अंश तथा हर को ${\cos \frac{A}{2}}$ से भाग देने पर )
$ = \tan \left( {\frac{\pi }{4} + \frac{A}{2}} \right)$.
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