# Expectation of an Hermitian operator is real.

1. Oct 30, 2007

### noospace

1. The problem statement, all variables and given/known data

WTS $\langle \hat{A} \rangle = \langle \hat{A} \rangle^\ast$

3. The attempt at a solution

$\langle \hat{A} \rangle^\ast = \left(\int \phi_l^\ast \hat{A} \phi_m dx\right)^\ast=\left(\int (\hat{A}\phi_l)^\ast \phi_m dx\right)^\ast= \int \phi_m^\ast \hat{A}\phi_l dx$. So far, I haven't seen why this equals $\int \phi_l^\ast \hat{A} \phi_m dx$.

Thanks

2. Oct 30, 2007

### mjsd

use same fields to show
eg. $$(\Psi, A\Psi) = (\Psi, A\Psi)^*$$