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$$\begin{gathered} Find \frac{dy}{dx} when : \\ \mathbf{\left(}\mathit{v}\mathit{i}\mathbf{\right)}\mathbf{ } y = 2 {\tan }^{-1} \sqrt{\frac{x - a}{b - x}} \\ \mathbf{4}\mathbf{.}\mathbf{\left(}\mathit{v}\mathit{i}\mathbf{\right)}\mathbf{ }\mathbf{ }\mathit{A}\mathit{n}\mathit{s}\mathbf{ }\mathbf{:}\mathbf{ }\frac{1}{\sqrt{\left(x - a\right) \left(b - x\right)}} \end{gathered}$$