x³+8y³-2x²y-4xy²=x³+(2y)³-2xy(x+2y)=
=(x+2y)(x²-2xy+4y²)-2xy(x+2y)=(x+2y)(x²-2xy+4y²-2xy)=
=(x+2y)(x²-4xy+4y²)=(x+2y)(x-2y)²
x³+8y³-2x²y-4xy²=x³+(2y)³-2xy(x+2y)=
=(x+2y)(x²-2xy+4y²)-2xy(x+2y)=(x+2y)(x²-2xy+4y²-2xy)=
=(x+2y)(x²-4xy+4y²)=(x+2y)(x-2y)²