Attachment 26007

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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- Dec 1st 2012, 11:01 AMkingsolomonsgravecomputing variance
Attachment 26007

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) - Dec 1st 2012, 11:43 AMScopurRe: computing variance
$\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.