Bonjour esque vous pouvez m’aider à mon dm de math niveau 3 eme

Bonjour,
1) D = (2x+3)²-(x+4)² = (4x²+12x+9)-(x²+8x+16)
= 4x²-x²+12x-8x+9-16
= 3x²+4x-7
2) D = (2x+3)²-(x+4)² = [(2x+3)+(x+4)][(2x+3)-(x+4)] car a²-b² = (a+b)(a-b)
= (3x+7) (x-1)
3) si x=6 alors D = (3(6)+7)(6-1) = 125
si x=-3/5 alors D = (3(-3/5)+7)(-3/5-1) = ((-9/5)+7)(-8/5)
= (-9/5 + 35/5)(-8/5)
= (26/5)(-8/5)
= -208/25