For the system of Prob. 8.2, explain why the variation function ( = (2/l)1/2sin(2(x/l) gives an upper

Question:

For the system of Prob. 8.2, explain why the variation function ( = (2/l)1/2sin(2(x/l) gives an upper bound to the energy E2 of the first excited state. (With the origin at the center of the box, V is an even function.) Use this ( to evaluate the variation integral for V0 = 2/ml2 and compare with the true value E2 = 20.236042/ml2.