已知2x-2y-5=1

x+y=02x+1=0x=-0.5y=0.52(x+5y)=2*(-0.5+2.5)=4平方根=±2

很多数学符号,还是写出来方便.

把x-y=-3y+5的左边移到右边：x-y+3y-5=0所以：x+2y-5=0x+2y-1=4

答：x+y=-1,xy=-2-5（x+y)+(x-y)+x(xy+y)=-5x-5y+x-y+xy(x+1)=-4x-6y+(-2)(x+1)=-4x-6y-2x-2=-6x-6y-2=-6(x+y)

(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

因为(x-y)/(x+y)=3,则(x＋y)/(x－y)＝1/3则5(x-y)(x+y)-(x+y)/2(x-y)＝5*3-1/(3*2)=15-1/6=89/6

X^2表示平方X^2+4X+4+Y^2-2Y+1=0(X+2)^2+(Y-1)^2=0因为平方大于=0所以X+2=0Y-1=0X=-2Y=1X^2+Y^2=5

-5（x+y)+(x-y)+2(xy+y)=-5x-5y+x-y+2xy+2y=-4x-4y+2xy=-4（x+y）+2xy=-4×（-1）+2×（-2）=4+（-4）=0你有问题也可以在这里向我提问

因为-5|x-2y|≥08|y-1\2|≥0而-5|x-2y|+8|y-1\2|=0所以-5|x-2y|=08|y-1\2|=0x-2y=0y-1/2=0解得x=1y=1/2

∵1x+2y=5，∴2x+yxy=5，∴2x+y=5xy，∴原式=2x+y+xy4(2x+y)-3xy=5xy+xy4×5xy-3xy=6xy17xy=617．

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)=

这道题目还是在考察韦达定理的运用用伟大定理求出xy的值再代入代数式否则是求不出来的(x+y)^2=x^2+y^2+2xy=1x^2+y^2=5(x-y)^2=5-2(-2)=9下面分两种情况讨论1x-

已知x²+y²+5=2x+4y所以(x-1)²+(y-2)²=0故x=1,y=2所以（2x²-（x+y)(x-y))×((x+y-1)(x-y+1)+

4x=9yx=9/4*y(1)(x+y)/y=[(9/4)y+y]/y=(9/4+1)y/y=9/4+1=13/4(2)(y-x)/2x=[y-(9/4)y]/[2*(9/4)y]=(1-9/4)y/

(3x-2y)(4x-5y)-11(x+y)(x-y)+5xy=12x^2-23xy+10y^2-11x^2+11y^2+5xy=x^2-18xy+21y^2=x^2-10xy+21y^2-8xy=(

1）x-5y/x+y=2y-5y/2y+y=-12)x=3z/5,y=4z/52x²-3xy+2xz/2y²-4x²+z²=（18z²/25-36z&

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

1,-3再问：过程。。。再答：★（x²－2x)+（y²－4y）=5★（x－1）²+（y－2）²=1+4－5★（x－l）²=0,（y－2）²=

5x+xy-5y/x+2y-y?应该是：(5x+xy-5y)/(x+2xy-y)吧!解析：已知x分之1-y分之1=3,那么：(xy)分之(y-x)=3即y-x=3xy所以：(5x+xy-5y)/(x+

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