令a=x^2+y^2则a(a-2)+1=0a²-2a+1=0(a-1)²=0a-1=0a=1所以x^2+y^2=1
(x^2+y^2)(x^2+y^2-2)+1=0(x^2+y^2)^2-2(x^2+y^2)+1=0(x^2+y^2-1)^2=0x^2+y^2=1
