## Thomas' Calculus 13th Edition

$f_x=y+z$ $f_y=x+z$ $f_z=y+x$
Take the first partial derivatives of the given function. When taking a partial derivative with respect to x, treat y and z as constants, with respect to y, treat x and z as constants, and with respect to z, treat x and y as constants: $f_x=y+z$ $f_y=x+z$ $f_z=y+x$