已知X^2-2XY=47,3XY+4Y^2=-19,则3X^2+8Y^2=多少?

已知x-y=4xy,求2x+3xy-2y/x-2xy-y的值 已知x-y=4xy,求x-2xy-y分之2x+3xy-2y的值! 已知x-y=3xy,求5x+2xy-5y/x-4xy-y的值 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 已知x y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) 由已知x+y=-2,xy=3那么2(x+xy)-[(xy-3y)-x]-(-xy)等于多少? 已知2x+xy=10,3y+2xy=6.求4x+8xy+9y=? 已知xy^2=-2,求-xy（x^2y^5-xy^3-y)的值. 已知xy^2=-2 求-xy(x^2y^5-xy^3-y) 已知xy^2=-2xy(x^2y^5-xy^3-y) 已知2x-2y=xy,求代数式3x-4xy-3y分之xy的值 已知x+y=4,xy=-2,求代数式3(xy+2y)-(xy-6x)的值 已知x+y=4,xy=-2,求代数式3（xy+2y）-（xy-6x） 已知x/y=3/4 ,则3xy-2y/2x+4xy=? 已知x-y的绝对值等于4,xy=-3,xy^2+x^2y=? 已知x+y=4,xy=2,求x+y+3xy的值 已知x^2-xy=5,xy-y^2=-3求3(x^2-xy)-xy+y^2