# 5. If z = xyln(xy), then

5. If z = xyln(xy), then

(A) $x \frac{\partial z }{\partial x} +y \frac{\partial z }{\partial y} =0$

(B) $y \frac{\partial z }{\partial x} =x \frac{\partial z }{\partial y}$

(C) $x \frac{\partial z }{\partial x} =y \frac{\partial z }{\partial y}$

(D) $y \frac{\partial z }{\partial x} +x \frac{\partial z }{\partial y} =0$

Hint: