Bonsoir,
1)A= (x-3)(4-x) - (x-3)(1-2x)
=4x-x²-12+3x-(x-3-2x²+6x)
= -x²+7x-12-(-2x²+7x-3)
= -x²+7x-12+2x²-7x+3
=x²-9
2)A= (x-3)(4-x) - (x-3)(1-2x)
=(x-3)[4-x-(1-2x)]
=(x-3)(4-x-1+2x)
=(x-3)(x+3)
ou
On a
A= (x-3)(4-x) - (x-3)(1-2x)
=x²-9
=x²-3²
=(x-3)(x+3)
3)A= (x-3)(4-x) - (x-3)(1-2x)
=x²-9
=(-2)²-9
=4-9
= -5
4)A=0
(x-3)(x+3)=0 Si ab=0 donc a=0 ou b=0
x-3=0 ou x+3=0
x=3 ou x= -3
Et voilà! ;)
