Let's say that a curve in the plane is o dd+ if there is some point of rotational symmetry2 . That is, we can rotate the paper 180 degrees at that point and the curve pre-rotation wil l exactly coincide with the curve post-rotation. Prove that y = x,y = x3,y = (x + 3)3 + 5 are all odd. Prove that y = x2 is not odd.