1/a,1/b 1/c成等差数列2/b=1/a+1/c=(a+c)/(ac)b(a+c)=2ac（b+c）/a + (a+b)/c =[(b+c)c+(a+b)a]/(ac)=[a^2+c^2+b(a+c)]/(ac)=(a^2+c^2+2ac)/(ac)=(a+c)*(a+c)/(ac)=(a+c)*2/b=2(a+c)/b所以（b+c）/a (c+a)/b (a+b)/c...