问题描述：
x/(y+z)=y/(x+z)=z/(x+y)
x/(y+z)=y/(x+z)=z/(x+y)=(x+y+z)/[(x+z)+(x+y)+(y+z)]=1/2
y/(x+z)=z/(x+y)=（y-z）/【（x+z）-（x+y）】=-1
我知道这是两种情况做法一是x+y+z≠0
做法二是x+y+z=0
我的疑问是做法二在证明中那里用到了x+y+z=0
x/(y+z)=y/(x+z)=z/(x+y)=(x+y+z)/[(x+z)+(x+y)+(y+z)]=1/2
y/(x+z)=z/(x+y)=（y-z）/【（x+z）-（x+y）】=-1
我知道这是两种情况做法一是x+y+z≠0
做法二是x+y+z=0
我的疑问是做法二在证明中那里用到了x+y+z=0
问题解答：
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