I am relatively new to maple and am using it for a multivariate calculus class.

I want to define a function g(x,y) which is the derivative of f(x,y).

I am trying:

which is my function, and

which should be the derivative.

When I try g(x,y) I get

but when I try to put numerical values in the first argument, (eg: f(1,y) I get

"Error, (in g) invalid input: diff received 1, which is not valid for its 2nd argument"
Any tips?