1/4a+1/4b =(a+b)/4ab ≥(a+b)/(a+b)^2 =1/(a+b) 同理1/4b+1/4c≥1/(b+c) 1/4c+1/4a≥1/(c+a) 由以上三式可得1/2a+1/2b+1/2c≥1/(a+b)+1/(b+c)+1/(c+a)
