(1)x³-2x²=x²(x-2)
(2)a²-9b²=(a+3b)(a-3b)
(3)5x²y-20y³=5y(x²-4y²)=5y(x-2y)(x+2y)
(4)3a³b²-6a²b+3a=3a(a²b²-2ab+1)=3a(ab-1)²