Réponse :
(x+3)²-3(x²-9)-2(4x+12)+(x+3)=
on remarque que 3(x²-9) = 3(x-3)(x+3)
on remarque que (4x+12) = 4(x+3)-->2(4x+12) = 8(x+3)
(x+3)²-3(x²-9)-2(4x+12)+(x+3)
(x+3)²-3(x-3)(x+3)-8(x+3)+1(x+3)=
(x+3)[(x+3)-3(x-3)-8+1]=
(x+3)(x+3-3x+9-8+1)=
(x+3)(-2x+5)
Explications étape par étape