Answer
$\dfrac{dy}{dx}=\dfrac{\sin{x}\sin{y}}{\cos{x}\cos{y}}.$
Work Step by Step
$4\dfrac{d}{dx}(\cos{x}\sin{y})=\dfrac{d}{dx}(1)$
$4(-\sin{x}\sin{y}+\dfrac{dy}{dx}(\cos{y}\cos{x}))=0\rightarrow$
$\dfrac{dy}{dx}=\dfrac{\sin{x}\sin{y}}{\cos{x}\cos{y}}.$
