当x=1,y=3(x+y)2;x2+2xy+y2;

当x=2,y=1 求{(x2+y2)/(x2-2xy+y2)+(2)/xy÷[(1/x)-(1/y)]}÷(x+y)的值 已知2x=3y,求xy／(x2+y2)-y2／(x2-y2)的值 x(x-1)-(x2-y)=-3,求x2-y2-2xy的值 x（x-1）-（x2-y）=-3,求x2+y2-2xy的值 已知x(x-1)-(x2-y)=-3,求x2+y2-2xy的值 已知:x=3,y=-5,x2-2xy+y2/x2-y2的值是 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x2+4y2+x2y2-6xy+1=0,求 x4-y4/2x-y 乘 2xy-y2/xy-y2 除以（x2+y2/x 已知x-y+1,X2+Y2=25 求（x+y）2和x2-xy+y2的值 2x2+xy-3y2+x+4y-1因式分解 正整数x,y满足x2-y2=2xy,求x-y/x+y的值 整数x,y满足x2-y2=2xy,求x-y/x+y的值