## Thomas' Calculus 13th Edition

$f_x=2(xy-1)\times y$ $f_y=2(xy-1)\times x$
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: $f_x=2(xy-1)\times y$ $f_y=2(xy-1)\times x$