原式=(x³+y³)²-[3xy(x+y)]²
=[(x³+y³)+3xy(x+y)][(x³+y³)-3xy(x+y)]
=[(x+y)(x²-xy+y²)+3xy(x+y)][(x+y)(x²-xy+y²)-3xy(x+y)]
=(x+y)(x²-xy+y²+3xy)(x+y)(x²-xy+y²-3xy)
=(x+y)²(x²+2xy+y²)(x²-4xy+y²)
=(x+y)^4(x²-4xy+y²)