Réponses

  • Utilisateur Brainly
2014-09-08T20:16:43+02:00
X² + 2x + 1 = (x + 1)(5x - 7)
x² + 2x + 1 = 5x² - 7x + 5x - 7
x² + 2x + 1 = 5x² - 2x - 7
x² - 5x² + 2x + 2x + 1 + 7 = 0
- 4x² + 4x + 8 = 0
4x² - 4x - 8 = 0
x² - x - 2 = 0

Δ = b² - 4ac
Δ = 1 + 8
Δ = 9

\boxed{\boxed{x_1_,_2= \frac{-b \pm\sqrt\Delta}{2a} }} \\  \\  \\  \\ x_1= \frac{1-3}{2}=-1 \\  \\ x_2= \frac{1+3}{2}  =2