S=(a+b+c)/a+(a+b+c)/b+(a+b+c)/c =3+b/a+c/a+a/b+c/b+a/c+b/c =(b/a+a/b)+(c/a+a/c)+(b/c+c/b)+3当且仅当a=b=c=1/3时Smin=5