Réponse de l'exercice 4: (S'il y'a des erreurs, mettez les en commentaire, mais ça m'étonnerait.).
Exercice n°4 :
A = (x+3) (x+1)
=x*x+x*1+3*x+3*1
=x²+x*1+3*x+3*1
=x²+4x+3
B = (x+7) (x+2)
=x*x+x*2+7*x+7*2
=x²+2x+7x+14
=x²+9x+14
C = (x+2) (x-5)
=x*x+x*(-5) +2*x+2*(-5)
=x²+(-5x)+2x+(-10)
=x²-5x+2x-10
=x²-3x-10
D = (x+3) (x-9)
= x*x+x*(-9) +3*x+3*(-9)
= x²+ (-9x)+3x+ (-27)
= x²-9x+3x-27
=x²-6x-27
E = (x+6) (x-8)
= x*x+x*(-8)+6*x+6*(-8)
=x²+(-8x)+6x+(-48)
=x²-8x+6x-48
=x²-2x-48
F = (x-3) (x+4)
= x*x+x*4-3*x-3*4
= x²+4x-3x-12
=x²+x-12
G = (x-7) (x-4)
= x*x+x*(-4)-7*x-7*(-4)
= x²+(-4x)-7x+28
= x²+(-11x)+28
=x²-11x+28
H = (x-1) (x+7)
= x*x+x*7-1*x-1*7
= x²+7x-x-7
= x²+6x-7
I = (2x+7) (3x+8)
= 2x*3x+2x*8+7*3x+7*8
= 6x+2x*8+21x+56
= 8x+21x+56*8
= 29x+ 448
