Réponse :
EX 3
A=(2x²-6x-4)-(5x-x²-4)
=2x²-6x-4-5x+x²+4
=3x²-11x
B=x-(-y+5)-5
=x+y-5-5
=x+y-10
C=(x-5)-(-y-5)
=x-5+y+5
=x+y
D=-(z²+2-4z)+(2z²-4z+1)
=-z²-2+4z+2z²-4z+1
=z²-1
E=-3(z²+5)+2(-4z+3)
=-3z²-15-8z+6
=-3z²-8z-9
F=1-5(2z²+8z-4)+3(z²-2z+10)
=1-10z²-40z+20+3z²-6z+30
=-7z²-46z+51
EX 4
on a G=5(x+y)+5(x-y)
et on x =-1/10 et y=-7,5/4
donc G=5(-1/10- (-7,5/4))+5(-1/10-7,5/4)
donc g=5(-1/10+7,5/4)+5(-1/10-7,5/4)
G=-5/10+37,5/4+(-5/10)-37,5/4
G=-10/10=-1
EX 5
A=(x+5)(x+2)
a=x²+2x+5x+10
a=x²+7x+10
b=(y+5)(3y-2)
b=3y²-2y+15y-10
b=3y²+13y-10
c=(4x-5)(7-3x)
c=28x-12x²-35+15x
c=-12x²+43x-35
d=(3x-7)(3x+7) identité remarquable n°3
d=9x²-49
EX 6
a=(6a-3a²)-(8a²+7a-6)-(12-8+3a²)
a=6a-3a²-8a²-7a+6-12+8-3a²
a=-14a²-a+2
b=7(5x-3)-4(3x²-1)-2x(3x+7)
b=35x-21-12x²+4-6x²-14x
b=-18x²+21x-17
c=(3y-4)(4y-3)-(-11y-3)(-2y+5)
c=12y²-9y-16y+12-(22y²-55y+6y-15)
c=12y²-9y-16y+12-22y²+55y-6y+15
c=-10y²+24y+27