x^4-y^4-4x²+4y²=(x²+y²)(x²-y²)-4(x²-y²)=(x²-y²)(x²+y²-4)=(x+y)(x-y)(x²+y²-4)=0x+y=0或x-y=0或x²+y²=4两条相交直线和一个圆...