Let U(x, y) be a potential. Are the following potentials separable in (a) cartesian coordinates, (b) polar coordinates? Explain your reasoning. 1) U(x, y)= x + y 2) (x+12) U(x, y)= e 2a2 3) 0 iff xa and |y| < a Vo otherwise 4) 0 iff x + y