c a b --- = --- = --- = k 求 k 的值.1a+b b+c a+c -1 或 --- 我要2-1

c/(a+b)=a/(b+c)=b/(a+c)=k,
(a+b)/c=(b+c)/a=(a+c)/b=1/k,
(a+b+c)/c=(a+b+c)/a=(a+c+b)/b=1/k+1
所以a=b=c或a+b+c=0
a=b=c时,(a+b+c)/c=3=1/k+1,k=1/2
a+b+c=0时,(a+b+c)/c=0=1/k+1,k=-1