[(x3-x2)+(x2-x1)]*[(x3+x2)+(x2-x1)](adsbygoogle = window.adsbygoogle || []).push({});

the book expands it to:

(x3-x2)^2+2(x3-x2)*(x2-x1)+(x2-x1)^2

i didnt get it so can someone please help me in this, i think there is a mistake in the book.

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# Formula for a square

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