# Finding average <x>

1. Oct 31, 2009

### z00maffect

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

What is the average <x> for following probability densities

P(x) = A[a$$^{4}+(x-x_{0})^{4})]^{-1}$$

2. Relevant equations

3. The attempt at a solution

dont know how to start

2. Oct 31, 2009

### meanyack

use this integration
$$\int_{a}^{b}\left|P(x)\right|^{2}*x*dx$$
in the given interval [a,b]
At least, we're doing so in quantum meachanics

3. Oct 31, 2009

### meanyack

I forgot to say that you must normalize this function ie
$$\int_{a}^{b}\left|P(x)\right|^{2}*dx=1$$
if the interval is not given you'll probably use $$[-\infty,\infty]$$.
So that you can determine the constant "A".

4. Nov 2, 2009

### criz.corral

Hi!

I think you don't need to take the square of P(x) because he's already probability density.

You normalize the probability density to find A:

$$\int_{-\infty}^{\infty}P(x)dx = 1$$

And then, the mean value of x ( <x> ) is:

$$\int_{-\infty}^{\infty}P(x)x dx$$

Last edited: Nov 3, 2009