Factoring Backwards (a – b)2

Find the value of this expression without using a calculator and without doing a lot of work. (Use your algebra eyes to see what’s going on.)

(1379)2 – (2) · (1379) · (379) + (379)2


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Observe: this seems to be in the form x2 – 2xy + y2 = (xy)2.

So, let x = 1379 and y = 379. Then xy = 1000.

So 13792 – 2(1379)(379) + 3792 = (1379 – 379)2 = 10002 = 1,000,000.

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