解:选Ca+b+c=0,则a+b=-c,a+c=-b,b+c=-a分别平方,得:a²+b²+2ab=c²,a²+c²+2ac=b²,b²+c²+2bc=a²于是有 a²+b²-c²=-2ab,a²+c²-b²=-2ac,b²+c²-a²=-2bc从而1/(b²+c²-a²)+1/(c²+a²-b²)+1/(a²+b²-c²)=-1/(2bc)-1/(2ac)-1/(2ab)=-1/2(1/bc+1/ac+1/ab)=-1/2(a+b+c)/abc=-1/2*0/abc=0