For the sake of simplicity, divide this equation thru by 2 to obtain
sinx cos y = 1/2.
Note that sinx cosy is a product, so apply the product rule:
(sin x) (-sin y dy/dx) + (cos y)(cos x) = 0
Solve this for dy/dx:
(sin x)(sin y) (dy/dx) = cos x cos y
cos x cos y
Then dy/dx = ------------------- (answer)
sin x sin y
