Réponse :
on factorise:
C = x² - 7
C= (x*x) - (√7 * √7) on utilise :a² -b² = (a -b)(a+b)
C = (x-√7)(x +√7)
D = 25x² - 1
D = (5x)² - (1)²
D = (5x - 1)(5x +1)
B = 81 - 4t²
B = 9² - (2t)²
B = (9-2t)(9+2t)
A = 18x² - 45
A = (3*2*2*x*x) - (3*3*5)
A = ((√3)² * 2² *x²) - (3² *(√5)²)
A = (2√3x)² - (3√5)²
A = (2√3 - 3√5)(2√3 + 3√5)
