Bonjour quelqu'un pourrait il m'aider pour l'exercice 85 svp

1) A(x) = (3+5x)²-(4x-7)(3+5x)
A(x) = 9+30x+25x²-(12x+20x²-21-35x)
A(x) = 9+30x+25x²-(20x²-23x-21)
A(x) 9+30x+25x²-20x²+23x+21
A(x) = 5x²+53x+30
2)
A(x) = (3+5x)²-(4x-7)(3+5x)  on met 3+5x en facteur
A(x) = (3+5x)(3+5x-4x+7)
A(x) = (3+5x)(x+10)
3)
a)
A(x) = 0
(3+5x)(x+10) = 0
⇔ 3+5x = 0 ou x+10 = 0
⇔ 5x = -3 ou x = -10
⇔ x =-3/5 ou x = -10
b)
A(x) = 30
⇔5x²+53x+30 = 30
⇔5x²+53x = 0
⇔x(5x+53) = 0
⇔x = 0 ou 5x+53 = 0
⇔x = 0 ou 5x = -53
⇔x= 0 ou x = -53/5

c)
A(x) = (3+5x)²
(3+5x)²-(4x-7)(3+5x) = (3+5x)²
⇔ -(4x-7)(3+5x) = 0
⇔4x-7 = 0 ou 3+5x = 0
⇔ 4x = 7 ou 5x = -3
⇔ x = 7/4 ou x = -3/5