Find dy/dx when y=0 if xcosy-sinx-2=0

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]