a/ 4x²-12x+9-(x-1)(3-2x)=4x²-12x+9-3x+2x²+3-2x
=6x²-17x+12
b/ 4x²-12x+9-(x-1)(3-2x)=(2x-3)²-(x-1)(3-2x)
a) 4x²-12x+9-(x-1)(3-2x)
=4x²-12x+9-(3x-2x²-3+2x)
=4x²-12x+9-3x+2x²+3-2x
=6x²-17x+12
b) On a 4x²-12x+9 qui se factorise en : (3-2x)² (car delta=3/2)
Donc au final on a
(3-2x)²-(x-1)(3-2x)
=(3-2x)(3-2x)-(x-1)(3-2x)
=(3-2x)(3-2x-x+1)
=(3-2x)(-3x+4)