一解下列方程组6(x-y)-7(x+y)=21;2(x-y)-5(x+y)=-1

问题描述:

一解下列方程组6(x-y)-7(x+y)=21;2(x-y)-5(x+y)=-1

①6(x-y)-7(x+y)=21;.
②2(x-y)-5(x+y)=-1
①-3②得x+y=3,带入①中,得x-y=7
x=5,y=-2①-3②得什么意思?①就是6(x-y)-7(x+y)=21;.②就是2(x-y)-5(x+y)=-1 ①-3②就是6(x-y)-7(x+y)-3【2(x-y)-5(x+y)】=21-3(-1)