Expectation Value in Inf. Box in an Eigenstate

[EnershyMethod]

Homework Statement

Obtain an expression for the expectation value <P_xⁿ>_n N=1,2... of a particle in an infinite box ( V=$$\infty$$ for x<0 and x>L ; V=0 for 0<X<L) which is in an eigenstate of the energy.

Homework Equations

P_n =+- $$\sqrt{2*m*En }$$ = +- (n*pi*Hbar) / L

The Attempt at a Solution

I don't know how to approach the problem because I am not sure what the notation of P is in the question. I included that formula because it is the closest formula I could find.

How can I approach this? Thanks.

 

[EnershyMethod]

BUMP,
We need it for tomorrow.