Consider the spring model " + 33 %3D 0, where the linear part of the spring is repulsive rather than attractive (for a normal spring it is attractive). Rewrite this as a system of first-order equations in x and y = x' . x' = y' Write down your system when you have it correct, for use in the next three problems. Then find all critical points and enter them below, in order of increasing x coordinate. (x.y) = (-U; (x,y) = (.): (x,y) =( For reference for the next three problems, write down your critical points after you've gotten them all right.