写得不规范啊是x^2+xy-2吧点(x,y)到原点的距离是2推出x^2+y^2=4三角代换x=2sinx,y=2cosxx^2+xy-2=4sin^2x+4sinxcosx-2=2(1-cos2x)+2sin2x-2=2(sin2x-cos2x)=(2sqrt2)sin(2x-pi/4)-2sqrt2