# What kind of question is it?

1. ### roshan2004

140
In my terminal exam I was asked to prove it that the parity operation commutes with Hermitian operator? I wonder how can we show that? coz we can only show that the parity operator is hermitian? We haven't got the value of hermitian operator at all?

2. ### Petr Mugver

280
On wave functions the parity operator acts something like

$$P\psi(x)=\eta\psi(-x)$$

where \eta is a phase factor independent of x. Now it should be easy to prove all the commutation relations you need.

3. ### roshan2004

140
Pls Can you show it to me how?

4. ### Petr Mugver

280
I can try, but first you have to tell me which is the operator you want to calculate the commutator with parity.

5. ### roshan2004

140
Hermitian operator

6. ### Petr Mugver

280
It's not enough. For example, P does not commute with the coordinates x or the momenta p (these anticommute with parity), but it commutes with orbital agular momentum or spin...

7. ### roshan2004

140
So, wasn't the question a wrong one?

8. ### the_house

134
If it really implied that the parity operator commutes with all Hermitian operators, then yes, it was wrong.