证明：因为a+b+c=0,则b=-(a+c),1/a+1/b+1/c =（bc+ac+ab）/abc =[(a+c)b+ac]/abc =[-(a+c)(a+c)+ac]/abc =-(a^2+ac+c^2)/abc =-[(a+c/2)^2+c^2*(3/4)]/abc,因为-[(a+c1/2)^2+c^2*(3/4)]0.