Répondre :
Bonjour,
x² + 10x + 9 = 0
⇔ x² + 2 * x * 5 + 5² - 25 + 9 = 0
⇔ (x + 5)² - 16 = 0
⇔ (x + 5)² - 4² = 0
⇔ (x + 5 + 4) (x + 5 - 4) = 0
⇔ (x + 9) (x + 1) = 0
⇔ x = -9 ou x = -1
Bonjour,
x² + 10x + 9 = 0
⇔ x² + 2 * x * 5 + 5² - 25 + 9 = 0
⇔ (x + 5)² - 16 = 0
⇔ (x + 5)² - 4² = 0
⇔ (x + 5 + 4) (x + 5 - 4) = 0
⇔ (x + 9) (x + 1) = 0
⇔ x = -9 ou x = -1