# Thread: Help with a couple of questions.

1. ## Help with a couple of questions.

Show How:

$\sigma x^2=(\sum \frac{x_i^2}{N})-\mu x^2$

Becomes:

$\sigma x^2=\sum \frac{(x_i - \mu x)^2}{N}$

I know how to do it the other way, but now it's asking me to do it this way and i'm confused.

Also, show how: $\sigma x^2=\sum \frac{x_i^2}{N} - (\frac {\sum x_i}{N})^2$

Becomes: $\sigma x^2=(\sum \frac{x_i^2}{N})-\mu x^2$

Lastly, show how: $\sigma x^2=(\sum \frac{x_i^2}{N})-\mu x^2$

Becomes: $\sigma x^2=\sum \frac{x_i^2}{N} - (\frac {\sum x_i}{N})^2$

I don't quite understand the expanding and/or simplifying i'm supposed to do. Any help is greatly appreciated.

2. ## Re: Help with a couple of questions.

Hey ANH13.

What is x^2? Is it a random variable or just a constant? Is it related in some way to the x_i's?

3. ## Re: Help with a couple of questions.

It's just x squared.

4. ## Re: Help with a couple of questions.

Your notation is a little confusing.

Are you trying to find sigma^2 * x^2 or are you trying to find the variance of the random variable x^2?

You need to really fix this up before we continue because it is full of ambiguities.