因为:
a/(a+1)=[x/(y+z)]/[(x+y+z)/(y+z)]=x/(x+y+z)
b/(b+1)=[y/(x+z)]/[(x+y+z)/(x+z)]=y/(x+y+z)
c/(c+1)=[z/(x+y)]/[(x+y+z)/(x+y)]=z/(x+y+z)
所以
a/(a+1)+b/(b+1)+c/(c+1)=x/(x+y+z)+y/(x+y+z)+z/(x+y+z)=(x+y+z)/(x+y+z)=1
因为:
a/(a+1)=[x/(y+z)]/[(x+y+z)/(y+z)]=x/(x+y+z)
b/(b+1)=[y/(x+z)]/[(x+y+z)/(x+z)]=y/(x+y+z)
c/(c+1)=[z/(x+y)]/[(x+y+z)/(x+y)]=z/(x+y+z)
所以
a/(a+1)+b/(b+1)+c/(c+1)=x/(x+y+z)+y/(x+y+z)+z/(x+y+z)=(x+y+z)/(x+y+z)=1