Réponses

Meilleure réponse !
2014-03-28T18:50:59+01:00
x²-x-2 = 0

Δ = b²-4ac
Δ = (-1)²-4*1*(-2)
Δ = 1+8
Δ = 9

Δ > 0

x
₁ = (-b-√Δ)/2a = [-(-1)-√9]/2*1 = (1-3)/2 = -2/2 = -1
x₂ = (-b+√Δ)/2a = (1+3)/2 = 4/2 = 2

factorisation pour Δ > 0 : a*(x-x₁)(x-x₂)

x²-x-2 = 1*(x+1)(x-2)
x²-x-2 = (x+1)(x-2)