(c) Let $u = \sin{x\ \ \ \ \ and\ \ v = \cos x}$ On differentiating w.r.t. $x$ respectively, we get $\ \frac{du}{dx} = \cos{x\ \ and\ \ \frac{dv}{dx} = - \sin x}$ $\therefore\ \frac{du}{dv} = \frac{du/dx}{dv/dx} = \ - \cot x$
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