如果x分之1=2Y(XY不为零)-搜答案-拍题作业网

不对.原命题的否定是：若XY=0,则X,Y都不为零.原命题的否命题是：XY不等于零,则X、Y都不为零.

由1/x-1/y=3得(y-x)/xy=3题中的式子分子分母同时除以xy得(2/y+3-2/x)/(1/y-2-1/x),通分得【2(x-y)/xy+3】/【(x-y)/xy-2】代入得3/5

∵x²-2xy-3y²=0∴*(x-3y)(x+y)=0∴x=3y或x=-y（1）2x+y/x-2y当x=3y时,原式=7y/y=7当x=-y时,原式=y/(-3y)=-1/3(2

x+y=3xy可得(x+y)/xy=3,得1/y+1/x=3答案就是3

xy/（x+y）上下同除以xy,得到1/（1/y+1/x）=5,则（1/x）+（1/y）=1/5

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

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

若x大于零,y大于零,且x分之2加y分之1等于11=2/x+1/y>=2√(2/xy)1>=8/xyxy>=8xy的最小值是=8

你传错了吧,怎么无解啊~

（x+2y-3xy)-(-2x-y+xy)=x+2y-3xy+2x+y-xy=(1+2)x+(2+1)y-(3+1)xy=3x+3y-4xy=3(x+y)-4xy=3*1/2-4*(-1/2)=3/2

1/x-1/y=(y-x)/xy=3所以y-x=3xy代入后面的公式得(-5xy)/(-9xy)=5/9

1.若x分之1-y分之1=2,则求x-xy-y分之3x+xy-3y=0的值.若x分之1-y分之1=2变形（y-x）/xy=2,(y-x)=2xy(3x+xy-3y)/(x-xy-y)=[3(x-y)+

1/x-1/y=3(y-x)/xy=3y-x=3xy分式的分母=x-2xy-y=(x-y)-2xy=-5xy分子=2x+3xy-2y=2(x-y)+3xy=-3xy所以原式=3/5

2x+3y-3xy+4xy-3x-4y+7=(2x-3x+3y-4y)+4xy-3xy+7=(-x-y)+xy+7=-(x+y)+xy+7=-4-1+7=2

由题可得（2x-y）/（3y）=y/x则：2x²-xy-3y²=0（2x-3y）（x+y）=0则2x-3y=0或者x+y=02x=3y或者x=-y所以：y分之x=3/2或者y分之x

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)=

正比例5x-4y=04y=5xy=4分之5x∴xy成正比例

x/y=2则x=2y代入下式(x^2+y^2)/xy=（4y^2+y^2）/(2y^2)=5/2

因为xy是不为零的有理数将（3+√5）x-（2-3√5）y=5-2√5拆开的话就能得到3x-2y=5x+3y=-2联立得：x=1;y=-1;x-2y=3平方根当然就是正负根号三了~~