已知x+y=2,则：(x²-y²)² -8(x²+y²）=[(x+y)(x-y)]²-8(x²+y²）=4(x-y)²-8(x²+y²）=4(x²-2xy+y²-2x²-2y²)=4(-x²-2xy-y²)=-4(x...