\sqrt{\frac{1-\cos A}{1+\cos A}}=\frac{\sin A}{1+\cos A}
Solution:
In LHS after rationalising, we can apply the identity sin2 A + cos2A =1
L. H. S. = \sqrt{\frac{1-\cos A}{1+\cos A}}
Rationalising the denominator
\begin{aligned} &=\sqrt{\frac{(1-\cos A)(1-\cos A)}{(1+\cos A)(1-\cos A)}} \\ &=\sqrt{\frac{(1-\cos A)^{2}}{1-\cos ^{2} A}}=\sqrt{\frac{(1-\cos A)^{2}}{\sin ^{2} A}} \\ &=\frac{1-\cos A}{\sin A}=\frac{1}{\sin A}-\frac{\cos A}{\sin A} \\ &=\operatorname{cosec} A-\cot A=\text { R.H.S. } \end{aligned}
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