in the last line of the above, why is the last expression not 2ab sigma xy? why is it just ab when the line above says 2abCov(X,Y)
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$\displaystyle \sigma_{XY} = Cov(X,Y) $ Its just notation. For example $\displaystyle \sigma_x = Cov(x,x) = \sigma_{XX} $ Sorry i miss read you question. It looks like they have a typo.
Last edited by Scopur; Dec 1st 2012 at 11:45 AM.
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