已知x^2+xy=13,且xy+y2=12,求(x+y)(x-y)和（x+y）^2

已知x2+4y2+x2y2+1=6xy,则(x4-y4)/(2x2+xy-y2)*(2x-y)/(xy-y2)/(x2+y2/y)2= 已知x2-2xy=3y2且x,y为非零实数 求：（1）2x+y/x-2y (2)2x2-3y2+5xy/x2+xy+y2 已知2x2+5xy-3y2=0且xy不等于0,求x:y的值已知2x2+5xy-3y2=0且xy不等于0,求xy的值 已知x^2+xy=13,且xy+y2=12,求(x+y)(x-y)和（x+y）^2 已知x>y>0,且xy=1,求 (x2+y2)/(x-y)的最小值, 已知xy不等于0,且3x2-2xy-8y2=0,求x/y的值? 已知y/x=1/2,求(x2+2xy+y2)/﹙x2-xy-2y2)的值. 已知x2+4y2+x2y2-6xy+1=0,求 x4-y4/2x-y 乘 2xy-y2/xy-y2 除以（x2+y2/xy）2乘1/x+y的值 已知X2+XY=2,Y2+XY+5,求1/2X2+XY+1/2Y2的值?‘X’是未知数 已知x2+xy=3,xy+y2=-2,则2x2-xy-3y2= 已知x2-3xy=-5,xy+y2=3,求x2-2xy+y2. 已知x满足2x2+4x+y2=2xy-4 求：xy 已知x2+y2+2x－6y+10=0,求xy的值已知x+y+z=1,且xy+yz+xz=0,求x2+y2+z2的值 化简求值:3(xy-y2)-[-xy+2(y2+xy)]+2,其中x=-1 2 ,y=-1. 已知x+y=8,xy=12,求(1)x2y+xy2(2)x2-xy+y2(3)x-y 已知x>y>0且xy=1.求x2+y2/x-y的最小值及此时xy的值 已知x,y∈R,且1≤x2+y2≤2,z=x2+xy+y2,则z的取值范围是 已知x2+xy=7 y2+xy=2 求x-y的值