Question

苏教版七年级数学《暑假总动员》练习题求解

求满足方程组 2x-y-4m=0,14x-3y=20 ，且y值是x值的3倍的m的值，并求此时代数式xy/x+y 的值
好的会加分！

Answer 1

将Y=3X代入: 14X-3Y=20 得: 14X-9X=20, X=4; Y=12.
将X=4; Y=12.代入:2X-Y-4m=0, 8-12-4m=0, m = -1.
得：XY/(X+Y)=48/16=3.

Answer 2

解: 将Y=3X代入: 14X-3Y=20 得: 14X-9X=20, X=4; Y=12.
又将X=4; Y=12.代入:2X-Y-4m=0, 8-12-4m=0, m = -1.
答: X=4; Y=12.m =-1. XY/(X+Y)=16/16=1.