Simple problem on expectation value

1. Mar 16, 2012

spaghetti3451

I know that <Aψ|Aψ> = <A2>. Can anyone tell please tell me how you get one line to the another?

2. Mar 16, 2012

spaghetti3451

Ok so, <Aψ|Aψ> = <AAψ|ψ> because A is self adjoint (hermitian). What next?

3. Mar 16, 2012

Amok

$$\langle A\psi \mid A\psi \rangle = \langle \psi \mid A^{\dagger}A\mid \psi \rangle$$

If A is Hermintian:

$$\langle \psi \mid A^{\dagger}A\mid \psi \rangle = \langle \psi \mid A^{2}\mid \psi \rangle$$

And that's it :)