Identify 'A' in the following reaction: \(\text{2 A + (C\(_6\)H\(_5\)CH\(_2\))\(_2\)Cd $\xrightarrow{}$ 2 CH\(_3\)-C-CH\(_2\)-C\(_6\)H\(_5\) + CdCl\(_2\)} \)
If \[ y = \cot^{-1}\!\left(\sqrt{\frac{1-\sin x}{1+\sin x}}\right), \quad \text{then find} \quad \frac{dy}{dx}. \]