左边=(a+b+c)/(a+b)+(a+b+c)/(b+c)+(a+b+c)/(c+a)-3=0.5*(a+b+b+c+c+a)*[1/(a+b)+1/(b+c)+1/(c+a)]-3≥0.5*{3*[(a+b)(b+c)(c+a)]^1/3}*{3*[1/(a+b)*1/(b+c)*1/(c+a)]^1/3}-3=0.5*3*3-3=3/2
