Réponse :
Bonjour
Exercice 1
1) E = 0 ⇔ 4x(x+3) = 0 ⇔ 4x = 0 ou x+3 = 0
⇔ x = 0 ou x = -3
2) a) Pour x = - 2, F = (-2)² + 6×(-2) + 9 = 4 - 12 + 9 = 1
b) (x + 3)² = x² + 2×3×x + 3² = x² + 6x + 9 = F
3) a) E = 4x(x + 3) = 4x×x + 4x×3 = 4x² + 12x
b) E - F = 4x² + 12x - x² - 6x - 9 = 3x² + 6x - 9
c) E + F = 4x(x + 3) + (x + 3)² = (x + 3)(4x + x + 3) = (x + 3)(5x + 3)
Exercice 2
1) P = (x + 12)(x + 2) = x² + 2x + 12x + 24 = x² +14x + 24
2) Q = (x + 7)² - 25 = (x + 7)² - 5² = (x + 7 + 5)(x + 7 - 5) = (x + 12)(x + 2)
3) Le triangle ABC est rectangle en A.D'après le théorème de Pythagore, on a :
AC² = BC² - AB² = (x + 7)² - 5² = (x + 12)(x+2) (voir 2)) = x² + 14x + 24 (voir 1))