∵x/﹙y+z﹚=a,y/﹙z+x﹚=b,z/﹙x+y﹚=c
∴﹙y+z﹚/x=1/a,﹙z+x﹚/y=1/b,﹙x+y﹚/z=1/c
∴﹙y+z﹚/x+1=1/a+1 ∴﹙y+z+x﹚/x=﹙a+1﹚/a
∴x/﹙x+y+z﹚=a/﹙a+1﹚
同理y/﹙x+y+z﹚=b/﹙b+1﹚
z/﹙x+y+z﹚=c/﹙c+1﹚
∴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
∵x/﹙y+z﹚=a,y/﹙z+x﹚=b,z/﹙x+y﹚=c
∴﹙y+z﹚/x=1/a,﹙z+x﹚/y=1/b,﹙x+y﹚/z=1/c
∴﹙y+z﹚/x+1=1/a+1 ∴﹙y+z+x﹚/x=﹙a+1﹚/a
∴x/﹙x+y+z﹚=a/﹙a+1﹚
同理y/﹙x+y+z﹚=b/﹙b+1﹚
z/﹙x+y+z﹚=c/﹙c+1﹚
∴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