x^4-x²-y^4+y²=0
(x²+y²)(x²-y²)-(x²-y²)=0
(x²-y²)(x²+y²-1)=0
x²=y²,x²+y²=1
y=x,y=-x,x²+y²=1
所以是两条直线和单位圆