若1 x-1 y=3,求5xy 2xy-5y x-4xy-y的值-搜答案-大师作文网

1设3x=2y=z=k,x=k/3y=k/2z=k代入就行了2.2（x+y）=5(3x-2y)13x=12yx:y=13:12

实数x,y满足(x-y-5)的平方+/2x+3y+20/=0x-y-5=0(1),2x+3y+20=0(2)由（1）+（2）得3x+2y+15=03x+2y+1=-14

x=4,y=0.5,x+y=4.5(与人家的做法一样……)(1)解题思路是以S3为基准,用S3表示出S1,S2,S4即可.在三角形BCD中有：S2/S3=DF/CF,故S2=(DF/CF)S3;同理,

根据题意，分式xy2x+3y中的x，y都扩大5倍，∴5x•5y2×5x+3×5y=25xy10x+15y=5xy2x+3y；即分式的值是原式值的5倍．故选B．

因为x:y:z=3：4：5所以设x=3k,y=4k,z=5k(k≠0)(1)z/(x+y)=5k/(3k+4k)=5k/7k=5/7(2)x+y+z=63k+4k+5k=612k=6k=1/2x=3k

因为X-Y=1所以原式=x*1+y*（-1）+2013=x-y+2013=1+2013=2014

1/x+1/y=5两边乘以xy得y+x=5xy∴x+y=5xy3x+4xy+3y/x+3xy+y=[3(x+y)+4xy]/[(x+y)+3xy]=(15xy+4xy)/(5xy+3xy)=19xy/

x^5+x^4y+x^4+x+y+1=0x^4(x+y+1)+x+y+1=0(x^4+1)(x+y+1)=0然后因为x^4+1不可能等于0所以只有x+y+1=0x+y+1=03x+2y=1这两个公式,

(1)已知x+y=6,x²-y²=5,x^2-y^2=(x+y)(x-y)=5x-y=5/(x+y)=5/6（2）若x+y=3,x²+y²=5(x+y)^2=3

解∵/y+5/+(5x+1)²=0∴y+5=0.5x+1=0∴y=-5,x=-1/5原式=-6x+3y-{7x-(10y-4x)-x-2(3x-4y)}=-6x+3y-[7x-10y+4x-

x-y=1,x+y=-73（x+y)+20(x-y)-5=3×（-7）+20×1-5=-21+20-5=-6

因为(x+y)=1所以(x+y)^2=x^2+2xy+y^2=1因为x^2+y^2=3所以2xy=1-3=-2xy=-1(x+y)(x^2+y^2)=x^3+y^3+xy^2+yx^2=x^3+y^3

∵(x+y-5)²+√（x-y+1）=0∴x+y-5=0,x-y+1=0得x=2,y=3故√（-4x+3y）=√1=1

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

7y(x-3y)²-2(3y-x)³=7y(x-3y)²+2(x-3y)³=(x-3y)²[7y+2(x-3y)=(x-3y)²(7y+2X

题目是否抄错?应该是（2X-3XY+2Y）/（X+2XY+Y）吧?1/X+1/Y=5（Y+X）/XY=5X+Y=5XY(2X-3XY+2Y)/(X+2XY+Y)=〔2（X+Y）-3XY〕/（X+Y+2

由3x=4y得x:y=4:3=20:15由3/5y=1/3z得y:z=5:9=15:27x:y:z=20:15:27

得y-x=3xyx-y=-3xy原式=-15xy+2xy/-3xy-4xy=-13/-7=13/7

原式=x-x+x-x+……-x+(2-1+4-3+5-4+……+2008-2007-2009）y=0+(1×1004-2009)y=-1005y=1005/2