f(x,y)= sin[x/(1+y)]

1. df/dx means we differentiate the function with respect to x while y is constant

then df/dx = [1/(1+y)]*cos(x/(1+y).

2. Now for df/dy we differentiate with respect to y while x is constant

==> df/dy = cos(x/(1+y)* [ -x/(1+y)^2]

= -cos(x/(1+y)*[x/(1+y)^2