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Cel mai inteligent răspuns!
2014-02-16T14:41:12+02:00
Folosesti formula diferentei de patrate: x^2-y^2=(x-y)(x+y)

In cazul tau, x=5a+7 si y=2b

Si deci,
(5a+7)^2-4b^2=(5a+7)^2-(2b)^2=(5a+7+2b)(5a+7-2b)
=(5a+2b+7)(5a-2b+7)