x² -y² = (x + y)(x-y)
x² - 9 = x² - 3² = (x+3)(x-3)
4 - a² = 2² - a² = (2+a)(2-a)
9y² - 16z² = (9y + 16z)(9y- 16z)
25x² - 9y² = (25x +9y)(25y-9y)
a²b² - 49 = ab⁴- 7² = (ab²)² - 7² = (ab² +7)(ab² -7)
Am aplicat doar formula de calcul prescurtat
a² -b² = (a-b)(a+b)