xcos(y) --> For this part, use the product rule, which would mean
cosy - xsiny * dy/dx
sinx's derivative is just cosx, so we get as a final answer
cosy - xsiny * dy/dx - cosx =0
-xsiny *dy/dx = cosx - cosy
dy/dx = cosx - cosy / -xsiny
When y=0,
dy/dx = cosx - cosy / -xsiny
dy/dx = cosx - cos(0) / -xsin(0) [note: sin(0) =0]
dy/dx = undefined [since you can't divide by 0]