Hi all. I have a quick question(adsbygoogle = window.adsbygoogle || []).push({});

In this wikilink en.wikipedia.org/wiki/Positive-definite_matrix in the first example

I don't get how they get 2x1^2 -2x1x2+2x2^2-2x2x3+2x3^2 in the third line.

Can anyone bother to explain?

Thanks a lot

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# Positive definitive matrix in wikipedia

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