若y=3x x=2y则x y 在等于-搜答案-神马作文网

令x/3=y/4=z/5=k；则x=3k,y=4k,z=5k;(xy+yz+xz)/(xx+yy+zz)=(3k*4k+4k*5k+3k*5k)/(3k*3k+4k*4k+5k*5k)=(12+20+

题目有问题

解题思路：本题将化简后的方程式子利用完全平方公式改写成两个方程式再进一步解答即可解题过程：

-5x+2-3xy-5y因为xy=1所以原式=-5x-5y-1-5（x+y)-1因为x+y=3所以-15-1=-16

x+y=5,xy=-3,则x^2y+xy^2=xy(x+y)=-3*5=-15

原式可化简为xy(-x^2-y^2+2xy)=xy(-x^2-y^2-2xy+4xy)=xy(-(x+y)^2+4xy)注：-x^2-y^2-2xy=-（x+y）将1,2式代入得,3*（-（-5）^2

这题偶也不会饿,不过为什么一定要用轮换做,我最后2题就不是用轮换的,哈哈,饿,我好像飘太多次了,汗,我该闪了,可是左闪,还是右闪?不对应该是按右上发的叉闪(偶废话好多),闪!大叉偶来也>P.S请无视我

4xy=(x+y)^2-(x-y)^2xy=〔(x+y)^2-(x-y)^2〕÷4运用这个,在进行计算.

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

2.25再答：x=1.5,y=1.50

2/9再问：过程，谢谢再答：由题目得y/x=2/3xy/xx+yy-yy/xx-yy=y/x-(y/x)²=2/3-4/9=2/9

x2+y2-z2+2xy/x2-y2+z2-2xz=(x+y)2-z2/(x-z)2-y2=(x+y-z)(x+y+z)/(x-y-z)(x-z+y)=(x+y+z)/(x-y-z)然后就是代入了

（x+2y-xy)-(-2x-y+xy)=x+2y-xy+2x+y-xy=3x+3y-2xy=3(x+y)-2xy=3×0.5-2×(-0.5)=1.5+1=2.5

xy/(x+y)=2(x+y)/xy=1/21/x+1/y=1/2(3x-xy+3y)/(-x+3xy-y)=(3/y-1+3/x)/(-1/y+3-1/x)=[3(1/x+1/y)-1]/[(3-(

|x-y|=4,xy=-3(x+y)^2=(x-y)^2+4xy=14-12=2x+y=根2,-根2xy^2+x^2y=xy(x+y)=-3根2,3根2再问：(x+y)^2=(x-y)^2+4xy=1

1/x-1/y=5即,(y-x)/xy=5即,x-y=-5xy(3x-2xy-3y)/(x+xy-y)=[3(x-y)-2xy]/[(x-y)+xy]=(-15xy-2xy)/(-5xy+xy)=(-

x^2+x-x^2-y=3x-y=3(x-y)^2=9x^2+y^2-2xy=9(x^2+y^2)/2-xy=9/2

(x+y)²=x²+2xy+y²=(x²-2xy+y²)+4xy=(x-y)²+4xy=49所以x+y=±7x²y+xy²

2x=3y(y不等于0)x=3/2yx^2-y^2/2xy=(9/4y²-y²)÷(2×3/2y²)=5/4y²÷(3y²)=5/12

x(x+1)-(xx+y)=-3x^2+x-x^2-y=-3x-y=-3(xx+yy)/2-xy=(x^2+y^2-2xy)/2=(x-y)^2/2=(-3)^2/2=9/2再问：是对的吧！再答：当然