9(x-2y)的三次方-x的平方(x-2y)
=(x-2y)[9(x-2y)²-x²]
=(x-2y)[3(x-2y)+x][3(x-2y)-x]
=(x-2y)(4x-6y)(2x-4y)
=4(x-2y)(2x-3y)(x-2y)
=4(2x-3y)(x-2y)²