Chapter 14: Partial Derivatives - Section 14.3 - Partial Derivatives - Exercises 14.3 - Page 807: 15

$f_x=\frac{1}{x+y}$ $f_y=\frac{1}{x+y}$

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: $f_x=\frac{1}{x+y}\times1$ $f_y=\frac{1}{x+y}\times1$