若X+Y+Z=0,则[Y+Z]/X=[Z+X]/Y=[X+Y]/Z=-1,而XYZ≠0,故
(Y+Z)(Z+X)(X+Y)/XYZ=(-X)(-Y)(-Z)/(XYZ)=-1
若X+Y+Z≠0,则由合分比定理得
[Y+Z]/X=[Z+X]/Y=[X+Y]/Z=[Y+Z+Z+X+X+Y]/(X+Y+Z)=2
于是有Y+Z=2X,Z+X=2Y,X+Y=2Z,于是
(Y+Z)(Z+X)(X+Y)/XYZ=2X*2Y*2Z/(XYZ)=8
题目肯定是笔误.
若X+Y+Z=0,则[Y+Z]/X=[Z+X]/Y=[X+Y]/Z=-1,而XYZ≠0,故
(Y+Z)(Z+X)(X+Y)/XYZ=(-X)(-Y)(-Z)/(XYZ)=-1
若X+Y+Z≠0,则由合分比定理得
[Y+Z]/X=[Z+X]/Y=[X+Y]/Z=[Y+Z+Z+X+X+Y]/(X+Y+Z)=2
于是有Y+Z=2X,Z+X=2Y,X+Y=2Z,于是
(Y+Z)(Z+X)(X+Y)/XYZ=2X*2Y*2Z/(XYZ)=8
题目肯定是笔误.