x的三次方—2x的平方+x
=x(x²-2x+1)
=x(x-1)²
-x的三次方+2x的平方—x
=-x(x²-2x+1)
=-x(x-1)²
x的三次方y—xy
=xy(x²-1)
=xy(x+1)(x-1)
9x的平方—y的平—4y—4
=9x²-(y-2)²
=(3x+y-2)(3x-y+2)