If V (x) is an even function (that is, V(-x) = V (x)) then (x) can always be taken to be either even or odd. Hint: If y (x) satisfies Equation 2.5, for a given E, so too does (-x), and hence also the even and odd linear combinations y (x) (-x). %3D + V = E. [2.5] -- %3| 2m dx2