Thomas' Calculus 13th Edition

$f_x=-(x+y)^{-2}$ $f_y=-(x+y)^{-2}$
Rewrite the given equation into the form: $f(x,y)=(x+y)^{-1}$ Take the first partial derivatives of the given function. When taking a partial derivative with respect to x, treat y as a constant, and vice versa: $f_x=-(x+y)^{-2}$ $f_y=-(x+y)^{-2}$