Bonjour,
Soit A = (4x + 3)2 – (4x +3)(x - 5).
1. Expliquer pourquoi on a A= 12 x2 + 41x + 24.
A = (4x + 3)² – (4x +3)(x - 5)
A = 16x² + 24x + 9 - (4x² - 20x + 3x - 15)
A = 16x² + 24x + 9 - 4x² + 20x - 3x + 15
A = 16x² - 4x² + 24x + 20x - 3x + 9 + 15
A = 12x² + 41x + 24
2. Factoriser A.
A = (4x + 3)² - (4x + 3) (x - 5)
A = (4x + 3) [(4x + 3) - (x - 5)]
A = (4x + 3) (4x + 3 - x + 5)
A = (4x + 3) (3x + 8)
3. Résoudre l'équation :
(4x+3)(3x+8)= 0.
4x + 3 = 0 ou 3x + 8 = 0
4x = - 3 3x = - 8
x = - 3/4 x = - 8/3.
