If $\cos y = x \cos (a + y)$ with $\cos a \neq \pm 1$, then $\frac{dy}{dx}$ is equal to

Question

$\frac{\sin a}{\cos 2(a + y)}$

$\frac{\sin a}{\cos^2(a + y)}$

$\frac{\sin a}{\cos a}$

$\frac{\sin^2(a + y)}{\cos^2(a + y)}$

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