This document is an exercise that shows can it can be checked that the squared angular momentum operator L^2, which is equal to l(l+1) can be obtained by summing the average value of Lx^2+Ly^2+Lz^2 which initially seems counter-intuitive. It is evaluated on the Hydrogen wavefunctions for the n=2 and l=1 states, the exercise is extended to the case where spin is included.