1) développer A(x) = (3 x + 2)(x + 4) = 3 x² + 14 x + 8
2) factoriser B(x) = (4 x + 2)(4 + x) - (x - 1)(4 + x)
= (4 + x)(4 x + 2 - x + 1)
= (4 + x)(3 x + 3)
= 3(4 + x)(x + 1)
3) Résoudre A(x) = B(x) ⇔ (3 x + 2)(x + 4) = 3(4 + x)(x + 1)
⇔ (3 x + 2)(x + 4) - 3(4 + x)(x + 1) = 0
⇔ (x + 4)(3 x + 2 - 3 x - 3) = 0
⇔ - (x + 4) = 0 ⇒ x = - 4