Répondre :
Bonjour,
identité remarquable : a² - b² = (a + b)(a - b)
A = (5x - 1)² - 9
A = (5x - 1)² - 3²
A = (5x - 1 + 3)(5x - 1 - 3)
A = (5x + 2)(5x - 4)
identité remarquable :
a²-b² = (a+b)(a-b)
donc:
(5x-1)²- 9 = (5x-1)² - 3² = (5x-1+3)(5x-1-3) = (5x+2)(5x-4)