已知x-y=6,xy=-8,求x^2+y^2的值,求1/2（x+y+z)^2+1/2(x-y -已知x-y=6,xy=-8,求x^2+y^2的值,求1/2（x+y+z)^2+1/2(x-y -z)(x-y+z)-z(x+y)的值

已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知:x/y=-2,求x^2-2xy-3y^2/x^-6xy 已知X+y=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y 已知xy/x+y=2,求代数式8x-5xy+8y/-x+3xy-y的值 已知xy/x+y=6,求3x-2xy+3y/-x+3xy-y的值. 已知(xy)/(x+y)=6求(3x-2xy+3y)/(-x+3xy-y)的值. 已知x的平方+y的平方-8x+6y+25=0,求(x-y+4xy/x-y)(x+y-4xy/x+y) 已知x²+y²-8x+6y+25=0,求（x-y+4xy/x-y）（x+y-4xy/x+y） 帮个忙啦 已知x+y=-6 xy=8 求√y/x+√x/y 已知x^2-6xy+9y^2=0,求(x-y)/(x+y) 已知x+y=6,xy=4,求x^2y+xy^2的值~ 已知(1/x)-(1/y)=5,求(6x+7xy-6y)/(8y-9xy-8y) 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? 已知x.x+y.y+8x+6y+25=0,求代数式(x.x-4y.y)/(x.x+4xy+4y.y)-x/(x+2y)的值 已知xy=2,x-y=3,求（x+y）（x-y）-y^2-（6x^2y-2xy^2)/2y的值. 已知xy=2,x-y=3,求（x+y）（x-y）-y^2-（6x^2y-2xy^2)/2y的值. 已知xy=-2,x-y=3,求(x+y)(x-y)-y平方+(x-y)平方-（6x2y-2xy平方）/2y的值