Nêu a+b+c khác 0 thi theo tinh chat day ti sô bang nhau ta co. a/b+c=b/c+a=c/a+b=a+b+c/2(a+b+c)=1/2N êu a+b+c=0 thi b+c=-a; c+a=-b;a+b=-c. Nêna/b+c,b/c+a,c/a+b =-1
Vì =\(\frac{b}{a+c}\)=\(\frac{a}{b+c}\)\(\frac{c}{a+b}\)
Nên a=b=c
suy ra \(\frac{a}{b+c}\)=\(\frac{b}{a+c}\)=\(\frac{c}{a+b}\)
Vậy\(\frac{a}{b+c}\)=\(\frac{b}{a+c}\)=\(\frac{c}{a+b}\)= \(\frac{1}{2}\)