x³-3x²+6xy-12y²+8y³
=x³+8y³-3x²+6xy-12y²
=(x+2y)(x²-2xy+4y²)-3(x²-2xy+4y²)
=(x²-2xy+4y²)(x+2y-3)
x³-2x²+1
=x³-x²-(x²-1)
=x²(x-1)-(x+1)(x-1)
=(x-1)(x²-x-1)