Salut !
Ex. 8 :
a) x² + 2x + 1 = x² + 2*x*1 + 1² = (x+1)²
b) x² - 10x + 25 = x² - 2*x*5 + 5² = (x-5)²
c) x² + 12x + 36 = x² + 2*x*6 + 6² = (x+6)²
Ex. 9 :
a²-b² = (a+b)(a-b) donc :
a) x² - 81 = x² - 9² = (x+9)(x-9)
b) x² - 1 = x² - 1² = (x+1)(x-1)
c) 9x² - 4 = (3x)² - 2² = (3x+2)(3x-2)
