Bonjour,
1) A = (2x-3)²+(5-6x)(2x-3)
= (4x²-12x+9)+(10x-15-12x²+18x)
= 4x²-12x²-12x+10x+18x+9-15
= -8x²+16x-6
2) A = (2x-3)²+(5-6x)(2x-3)
= (2x-3)(2x-3)+(5-6x)(2x-3)
= (2x-3)[(2x-3)+(5-6x)]
= (2x-3)(-4x+2)
= -(2x-3)(4x-2)
= -2(2x-3)(2x-1)
3) A = 0
⇒ 2x-3=0 ou 2x-1=0
⇒ 2x=3 ou 2x=1
⇒ x=3/2 ou x=1/2
3) x=-1/2
⇒ A = -2(2(-1/2)-3)(2(-1/2)-1) = -16
