a+b+c=0
a+b=-c
两边平方,
a²+b²-c²=-2ab
b+c=-a
两边平方,
b²+c²-a²=-2bc
c+a=-b
两边平方,
c²+a²-b²=-2ca
1/(b²+c²-a²)+1/(c²+a²-b²)+1/(a²+b²-c²)
=-[1/(2bc)+1/(2ca)+1/(2ab)]
=-[(a+b+c)/(2abc)]
=0
a+b+c=0
a+b=-c
两边平方,
a²+b²-c²=-2ab
b+c=-a
两边平方,
b²+c²-a²=-2bc
c+a=-b
两边平方,
c²+a²-b²=-2ca
1/(b²+c²-a²)+1/(c²+a²-b²)+1/(a²+b²-c²)
=-[1/(2bc)+1/(2ca)+1/(2ab)]
=-[(a+b+c)/(2abc)]
=0