My TA did not get the chance to go over this problem. I know that I'm supposed to differentiate both sides of the equation. But I have not the slightest idea what to do after that. I was told that I am supposed to get out 4 points that lie on the ellipse and the sides of the box are tangent to the ellipse. Also, the horizontal lines have a slope of 0 but as for the vertical lines, i dont know. So how should I solve this problem? after differentiating, am i supposed to solve for y' or y? Any hints or tips? Thanks alot!