Ok, I have been working on this, but am still stuck. What am I doing wrong, or what do I need to do next:
GradF= Fx+F y +Fz
Ff = sin(2(x-y)) -sin (2(y-z))
Fz = -sin(2(z-x)) +sin(2(y-z))
But it seems to me like all of these terms cancel out if I add them together. So I do not know how to proceed.