2x分之一-x y分之一×(2x分之x y-x-y)=?

|xy-2|与|y-1|互为相反数,即|xy-2|+|y-1|=0xy-2=0,y-1=0所以x=2,y=1从而原式=1×2分之1＋2×3分之1＋3×4分之1＋.+2015×2016分之1=1-2分之

(x^2)/2+xy+(y^2)/2=1/2*(x^2+2xy+y^2)=(x+y)^2/2=1/2

由　1/X-1/Y=5,两边同乘　XY,得出Y-X=5XY,那么　　分子　-X+XY+Y=6XY分母　2X+7XY-2Y=7XY-2(Y-X)=-3XY　　得此分式的值为－再问：还有一题x+x分之一=

答：1/x+1/y=3(x-2xy+y)/(2x+xy+2y)分子分母同除以xy得：=(1/y-2+1/x)/(2/y+1+2/x)=(3-2)/(3*2+1)=1/7

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

√xy+y分之一+√xy+x分之一=√xy(1／x+1／y)=√xy乘[（x+y）／xy]=√xy（x+y）再问：√xy(1／x+1／y)这一步怎样计算？再答：(1／x+1／y)1／x和1／y通分再问

-2,前提是xy都不为零再问：能说一下解题步骤吗？

x分之1-y分之1=4(xy)分之(y-x)=4y-x=4xyx-y=-4xy(x-2xy-y)分之(2x+xy-2y)=[(x-y)-2xy]分之[2(x-y)+xy]=(-4xy-2xy)分之(-

1/X-1/Y=4Y-X=4XY(2X+XY-2Y)/(X-2XY-Y)=[2(X-Y)+XY]/[(X-Y)-2XY]=7/6

1/2x²+xy+1/2y²=1/2(x²+2xy+y²)=1/2(x+y)²=1/2

|x-1|+|y+3|=0|x-1|≥0|y+3|≥0所以x-1=0,y+3=0x=1,y=-3原式=1/1*-3+1/3*-1+1/1*5+1/3*7+1/5*9+.+1/(2n-1)(2n+3)=

x+2y=11/x+1/y=(x+2y)/x+(x+2y)/y=3+2y/x+x/y>=3+2*√2

x分之一减y分之一等于2分之1所以xy分之y-xy分之x=2分之1,xy分之（y-x）=2分之1,y-x=2分之xy,x-y=负2分之xy,所以x减y分之xy=（负2分之xy）分之xy=-xy分之（2

因为1/x-1/y=3所以方程左边先通分得y/xy-x/xy=3即（y-x）/xy=3所以得y-x=3xy（这一步很关键,一会要用整体代入法)要求的分数的分子：x+xy-y=xy-3xy=-2xy(因

x+y=6两边同时平方得x²+2xy+y²=36把xy=-2代入上式得x²+y²=401/x²+1/y²=y²/(x²y

1/xy+1/(x+1)(y+1)+1/(x+2)(y+2)+…+1/(x+2010)(y+2010)=1/（1*2）+1/（2*3）+1/（3*4）+.+1/（2011*2012)=1/1-1/2+

因为(x+1/y)(y+1/x)=xy+1+1+1/xy=18+2=20所以y+1/x=20/5=4再问：哦再问：我没想到，，，，

1/x+1/y=（x+y)/xy=5x+y=5xy所以原式=[2(x+y)-3xy]÷[(x+y)+2xy]=[2(5xy)-3xy]÷[(5xy)+2xy]=7xy÷7xy=1再问：1/x+1/y=

x+2y=11/x+1/y=(1/x+1/y)(x+2y)=1+x/y+2y/x+2≥3+2√2X分之一加Y分之一的最小值3+2√2

选择题最好的方法：设X=2,Y=1或X=-2,Y＝-1,则1/X+1/Y＝1/2+1＝1.5或1/X+1/Y＝－（1/2+1）＝-1.5