{80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 怎么解( ⊙ o ⊙ {80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 快 急
问题描述：
{80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 怎么解( ⊙ o ⊙
{80/(x+y) +42/(x-y) =7 40/(x+y) +70/(x-y) =7 快 急
答
把x+y和x-y看成两个整体，设x+y=a，x-y=b
算出ab为多少，然后再算x、y
答
把1/(x+y),1/(x-y)看成整体
可得 1/(x+y)=1/20 1/(x-y)=1/14
所以 x+y=20 x-y=14
x=17 y=3
答
这道题的思路很简单,就是一个二元方程组.首先把两个方程的左边项分别通分,两个方程的分母（x²-y²）和右边项（7）都一样,那么他们的分子也相等,也即122x-38y=110x+30y,由此把y用x表示,可以得到y=3x/17,把这...
答
1/(x+y)=1/20 1/(x-y)=1/14
x+y=20 x-y=14
x=17 y=3