1,已知:x+2y=7,xy=6,求(x-2y)的2次方的值 2,已知a+b=7,a的2次方+b的2次方=29,求（a-b）的2次方的值第1题的答案是1,第2题的答案是9,

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=-2,求x^2-2xy-3y^2/x^-6xy 已知1/x-1/y=5,求分式y+xy-x/2x+7xy-2y的值. 已知1/x-1/y=5 求分式-x+xy+y/2x+7xy-2y 已知1/X-1/y=5,求分式(y+xy-x)/(2x+7xy-2y)的值 已知x-y=6,xy=-1,求(2x+3x-2xy)-(x+4y+xy)-(3yx-2x+2y)的值 已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值. 已知(1/x)-(1/y)=5,求(6x+7xy-6y)/(8y-9xy-8y) 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3/(x-y)=1/xy 求(-x-2xy+y)/ (2x+3xy-2y) 已知xy-x-y=11,求(xy-1)^2+(x+y-2)(x+y-2xy)的值. 已知1/x - 1/y = 2,求3x+7xy-3y / 2x-3xy-2y的值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)=-1/71/x-1/y=2到(y-x)/xy=2 是怎么变化的.. 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 已知实数xy,满足10x²-2xy+y²+6x+1=0,求x+y 已知xy^2=-6,求-xy(x^3y^7-3x^2y^5-y）的值 已知,x-y=2,xy=7 求x^2 y-xy^2