Répondre :
A= 3x²-9x=3x(x-3)
B=36x²-81=9(4x^2-9)=9((2x)^2-3^2)=9(2x-3)(2x+3)
C=(2x+5)(x+1)+x(2x+5)=(2x+5)[(x+1)+x]=(2x+5)(2x+1)
D=(7+x)(4x-1)-(7+x)(x-2)=(7+x)[(4x-1)-(x-2)]=(7+x)(3x+1)
E=(x²+2x+1)+(x+1)(3x-5)=(x+1)^2+(x+1)(3x-5)=(x+1)[(x+1)+3x-5]=(x+1)(4x-4)=4(x+1)(x-1)
F=(x-5)²-9=(x-5)²-(3)^2=(x-5+3)(x-5-3)=(x-2)(x-8)