Math Calculus - please show all steps

2. The partial derivative of function f(x, y) with respect only to the independent variable r is defined as fx(x, y) = lim f(x + h, y) - f(x, y) h-0 h Use this definition to derive the partial derivative f, for the following functions. You may not use L'Hopital's Rule in your derivation of the limit nor any of the usual differentiation rules. A. f(x,y) = xy+ 2 B. f(x,y) = cos(ry)