Prove that sum that : Sum ( i=1 to N) of ( Xi-Xbar)/ N ((X^2)bar - (Xbar)^2) = 0
I have a hard time reading the post But this may help.
$\displaystyle \;\overline X = \dfrac{{\sum\limits_{n = 1}^N {x_n } }}
{N}\, \Rightarrow \,\,\sum\limits_{n = 1}^N {\overline X } = N\overline X = \sum\limits_{n = 1}^N {x_n } $
Yeah, as I said my brain just didn't want to work. I realized that the denominator in that fraction can be factored out (not dependent on i) and then its just very simple to proof that sum Xn-xbar=0.