a/(a+b)+b/(b+c)+c/(c+a)=1/2{[(a-b)+(a+b)]/(a+b)+[(b-c)+(b+c)]/(b+c)+[(c-a)+(c+a)]/(c+a)}
a/(a+b)+b/(b+c)+c/(c+a)=1/2[(a-b)/(a+b)+(b-c)/(b+c)+(c-a)/(c+a)]+3/2
(a-b)/(a+b)+(b-c)/(b+c)+(c-a)/(c+a)
通分得:(a-b)/(a+b)+(b-c)/(b+c)+(c-a)/(c+a)=-(a-b)(b-c)(c-a)/(a+b)(b+c)(c+a)=-5/132
所以:a/(a+b)+b/(b+c)+c/(c+a)=-1/2*5/132+3/2=391/264