解(1)x³-5x²-6x
=x(x²-5x-6)
=x(x-6)(x+1)
②a²-b²-2b-1
=a²-(b²+2b+1)
=a²-(b+1)²
=(a+b+1)(a-b-1)
3.[x-2x/(x+1)]÷(x²-2x+1)/(x²-1)
=[x(x+1)-2x]/(x+1)÷(x-1)²/(x+1)(x-1)
=(x²-x)/(x+1)÷(x-1)/(x+1)
=x(x-1)/(x+1)÷(x-1)/(x+1)
=x
4.：(a+b)(a-b)+(a+b)²-2a²
=a²-b²+a²+2ab+b²-2a²
=2ab
=2×3×(-1/3)
=-2