We prove the following two theorems: (i) Let be the th power mean of and . The inequality holds for all if and only if , where denotes Euler's constant. This refines results established by W. Gautschi (1974) and the author (1997). (ii) The inequalities are valid for all if and only if and , while holds for all if and only if and . These bounds for improve those given by G. D. Anderson an S.-L. Qiu (1997). |