Réponse :
Bjr,
1) A=(2 x+1)(x-3)+(2x+1)(3x+2) = 2x²+x-6x-3+6x²+4x+3x+2 = 8x²+2x-1
2) A=(2 x+1)(x-3)+(2x+1)(3x+2) = (2x+1)(x-3+3x+2) = (2x+1)(4x-1)
3) a) A = 0 ⇔ (2x+1)(4x-1) = 0
A = 0 ⇔ (2x+1) = 0 ou (4x-1) = 0
A = 0 ⇔ 2x = -1 ou 4x = 1
A = 0 ⇔ x = -1/2 ou x = 1/4
