Răspuns :
Folosim formula [tex] a^{2} - b^{2} =(a+b)(a-b)[/tex] si vom aveam:
(5a+7-2b)(5a+7+2b)
(5a+7-2b)(5a+7+2b)
(5a+7)²-4b²=5a²+2*(5a*7)+7²-4b²=25a²+2*(35a)+49-4b²=
=25a²+70a+49-4b²=a(25a+70)-4b²+49
(5a+7)²-4b²=(5a-2b+7)(5a+2b+7)
=25a²+70a+49-4b²=a(25a+70)-4b²+49
(5a+7)²-4b²=(5a-2b+7)(5a+2b+7)