x^3+8y^3+6xy>=1得x^3+(2y)^3+(-1)^3-3x2y(-1)>=0(这部看得懂）得x+2y-1=0这部怎么得到?和没讲一样

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+1)²+|y-1|=0,求2(xy-5xy²)-(3xy²-xy)得值 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 一个多项式叫上2x-3xy-3y+1得x-6xy-y求这个多项式 xy不等于0,且3x平方-2xy-8y平方=0,求x/y得值 x(x-1)-(x的平方-y)=-3,求(x+y)的平方-4xy得值 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 先化简,再求值：x^x+xy/x^x-xy^(y^y-xy/xy)除以(x+y),其中x=1/3,y=-3 已知1/x+1/y=3,求分式(3x-3xy+3y)/(x+xy+y)的值我知道第一步是两边都乘以xy得x+y=3xy,然后怎么代进去,求回答! 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y 4xy-[(x²+5xy-y²)-(3xy-1/2y)]x=3,y=-6 -3(2x-xy)-4(-6+xy+x.其中x=1,y=-1 已知x-y=6,xy=-1,求(2x+3x-2xy)-(x+4y+xy)-(3yx-2x+2y)的值 帮解下二元一次方程(x-6)*(y+3)=xy(x+4)*(y-1)=xy 已知1/x=1/y=6,则3x-2xy+3y/3xy+x+y=?已知1/x+1/y=6,则3x-2xy+3y/3xy+x+y=? -x-3xy+y