已知x+y=6,xy=7,求(3x+y)的平方+（x+3y)的平方的值

已知x+y=6,xy=7,试求x*x+y*y,x*x-y*y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/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xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y 已知x=3y,试求（x-y)^2+2xy-y^2/x^2+7xy+y^2 已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 已知X+Y=6,xy=3求代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)的值 已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值. 已知x+y=3,xy=6,.求根号x/y+根号y/x 已知xy^2=-6,求-xy(x^3y^7-3x^2y^5-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xy^2=-2求xy（2x^3y^7+5x^2y 已知x+y=6,xy=7,求(3x+y)*(3x+y)+(x+3y)*(x+3y)的值 已知(1/x)-(1/y)=5,求(6x+7xy-6y)/(8y-9xy-8y) 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.