a, x(x-5)-4x+20=x(x-5)-(4x-20)=x(x-5)-4(x-5)=(x-5)(x-4)
b, x(x+6)-7x-42=x(x+6)-(7x+42)=x(x+6)-7(x+6)=(x+6)(x+7)
c, x²-2xy+y²-xz+yz
=(x-y)²-z(x-y)
=(x-y)(x-y-z)
d,x²-y²-x+y
=(x+y)(x-y)-(x-y)
=(x-y)(x+y+1)
e, a³x-ab+b-x=(a³x-x)-(ab-b)=x(a³-1)-b(a-1)=x(a-1)(a²+a+1)-b(a-1)
=(a-1)(a²x+ax+x-b)
f, x²-x-6=x²-3x+2x-6=x(x-3)+2(x-3)=(x-3)(a+2)
g, x³-64= x³-4³=(x-4)(x+4x+16)
h, x³+6x²y+12xy²+8y³=(x+2y)³
i, 125x³+y^6= 125x³+(y²)³= (5x+y²)(25x²-5xy²+y^4)
k,3x²-12y²= 3(x²-4y²)=3(x-2y)(x+2y)=(3x-6y)(x+2y)
