How do I correctly evaluate <x^2> for a particle in a one-dimensional box?

[w3390]

Homework Statement

Consider a particle in an infinite one-dimensional box that has a length L and is centered at the origin. (Use h for Planck's constant, n, and L, as necessary.) Evaluate <x^2> for <x^2> at n=1.

Homework Equations

<x^2>= (2/L)[(L^3/24)-(L^3/4n^2*pi^2)cos(n*pi)]

The Attempt at a Solution

I used this formula and got the answer (L^2/12)+(L^2/(2*pi^2)). My assignment is telling me this is incorrect. I took the same approach for the second part of my homework asking for this when n=2, and I got (L^2/12)-(L^2/(8*pi^2)) which it says is correct. I cannot figure out why my first answer is not correct as well. Any help would be much appreciated.

 

[w3390]

Sorry. Just figured it out.