xy=10,x分之2 y分之5的最小值

原式=（2x+y）/（5xy-6xy）×（1/2）（x+2y）=（x+y）/（-xy）×（1/2）（x+y）=（-xy）/（2x+2y）=（-xy）/2(x+y)=（1/2）×（-xy）/(x+y)当

由xy/（x+y）=2,∴xy=2（x+y）∵（-x+2xy-y）/（3x-5xy+3y）=（-x-y+4x+4y）/3x+3y-10x-10y）=（3x+3y）/（-7x-7y）=-3/7.

1、答案：负七分之五解题：xy=2x+2y代入原式,整理合并同类项即可得出2、如果只考虑在同一平面内,有三条线.如图

解1/x+1/y=5即(y+x)/xy=5∴y+x=5xy∴(2x+3xy+2y)/(x-2xy+y)=[2(x+y)+3xy]/[(x+y)-2xy]=[2×5xy+3xy]/(5xy-2xy)=(

1/x-1/y=3x-y=-3xy(2x+3xy-2y)/(x-2xy-y)=[2(x-y)+3xy]/[(x-y)-2xy]=(-3xy)/(-5xy)=3/5

∵(x+y)分之xy=3∴xy=3(x+y)∴(-2x+3xy-2y)分之(3x-5xy+3y)=[-2(x+y)+9(x+y)]分之[3(x+y)-15(x+y)]=[7(x+y)]分之[-12(x

(5x+3xy-5y)/(x-2xy-y)=(5/y+3-5/x)/(1/y-2-1/x)分子分母同时除以xy=[-5(1/x-1/y)+3]/[-(1/x-1/y)-2]=(-15+3)/(-3-2

1/x-1/y=(y-x)/xy=3y-x=3xy所以x-y=-3xy所以原式=[(x-y)-2xy]分之[2(x-y)-5xy]=[(-3xy)-2xy]分之[2(-3xy)-5xy]=(-5xy)

1/x+1/y=-2则(x-xy+y)/(x+xy+y)分子分母同除以xy=(1/x+1/y-1)/(1/x+1/y+1)=(-2-1)/(-2+1)=3

xy/(x+y)=2∴xy=2(x+y)(3xy-x-y)/(3x-5xy+3y)=[6(x+y)-x-y]/[3x+3y-10(x+y)]=5(x+y)/[-7(x+y)]=-5/7

1/x+1/y=(x+y)/(xy)=5x+y=5xy(2x-3xy+2y)/(x+2xy+y)=(2*5xy-3xy)/(5xy+2xy)=(10-3)/(5+2)=1

因为X+Y分之XY=2,所以XY=2(X+Y)代入后面的分子式得：13（X+Y)/5(X+Y)=13/5

x+y分之xy=2,则xy/(x+y)=2xy=2x+2y(-x+3xy-y)分之(3x-5xy+3y)=(3x-5xy+3y)/(-x+3xy-y)=[3x-5(2x+2y)+3y)/[-x+3(2

1/x-1/y=(y-x)/xy=3y-x=3xy(2x-5xy-2y)/(3x-10xy-3y)=-8xy/-19xy=8/19自己算一下直接看着算的反正就是整体代入思想

因1/x+1/y=5(x+2xy+y)/(2x-3xy+2y)上下同乘以1/(xy)得[1/y+2+1/x]/[2/y-3+2/x]整理得[(1/x+1/y)+2]/[2(1/x+1/y)-3]将已知

(y-x)/xy=3y/xy-x/xy=3所以1/x-1/y=3(3x-5xy-3y)/(x-2xy-y)分子分母同时除以xy原式=(3/y-5-3/x)/(1/y-2-1/x)=[3(1/y-1/x

1/x-1/y=(y-x)/xy=2y-x=2xy(3x-5xy-3y)/(-x+3xy+y)={3(x-y)-5xy}/(y-x+3xy)={(-3)*2xy-5xy}/5xy=-11/5

x+y分之xy=2,则xy/(x+y)=2xy=2x+2y(-x+3xy-y)分之(3x-5xy+3y)=(3x-5xy+3y)/(-x+3xy-y)=[3x-5(2x+2y)+3y)/[-x+3(2

1/x+1/y=5(x+y)/x*y=5x+y=5*x*yx+2xy+y=x+y+2xy=5xy+2xy=7xy2x-3xy+2y=10xy-3xy=7xy(2x-3xy+2y)/(x+2xy+y)=

(3x+5xy-3y)/(x-xy-y)=(3x-3xy-3y+8xy)/(x-xy-y)=3+8xy/(x-xy-y)=3+8/(1/y-1-1/x)=3+8/(-3)=1/3