'vl 20. Show by direct substitution that Eq. 5.39 gives a solution to the two-dimensional Schrodinger equation, Eq. 5.37. Find the relationship between k , k, and E.y(x, y) = f(x)g(y) (5.39)h2 a2 ys ( x, y) a2 us ( x, y) + + U(x, y)us (x, y) = Ey(x, y) (5.37) 2m 0x2