1.-a+2a²-a³
=-a(1-2a+a²)
=-a(1-a)²
2.1-6y+9y²
=(1-3y)²
3.y²-4
=(y-2)(y+2)
4.2x³-6x
=2x(x²-3)
=2x(x+√3)(x-√3)