解
x³-4x²-12x
=x(x²-4x-12)
=x(x-6)(x+2)

第二题
3a³-6a²b+3ab²
=3a(a²-2ab+b²)
=3a(a-b)²

x²a-2ax+a
=a(x²-2x+1)
=a(x-1)²