X2+Y2+XY=2,求X2+Y2-XY取值范围

X2+Y2+XY=2,求X2+Y2-XY取值范围 x2+y2-xy=1,则u=x2-y2的取值范围是 已知2x=3y,求xy／(x2+y2)-y2／(x2-y2)的值 设x,y是实数,且 x2+xy+y2=3.那么,x2-xy+y2的取值范围是? 设x,y为实数,且x2+xy+y2=1,求x2-xy+y2的值的范围 设实数xy满足x2 +2y2=6,则x+y的取值范围 已知x、y是实数且满足x2+xy+y2-2=0，设M=x2-xy+y2，则M的取值范围是______． 实数x、y满足x2+xy+y2=2,记u=x2-xy+y2,则u的取值范围是 已知x2-xy=-3，2xy-y2=-8，求2x2+4xy-3y2的值． 已知x2+xy=-3，xy+y2=7，试求：x2+2xy+y2的值． 已知x2-xy=3，xy-y2=-5，试求代数式x2+2xy-3y2的值． 已知实数XY 满足X2+Y2=1,求Y+2/X+1的取值范围