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Inequalities for means in two variables. (English) Zbl 1020.26011
Summary: We present various new inequalities involving the logarithmic mean $L(x,y) = (x-y)/(\log x-\log y)$, the identric mean $I(x,y) = (1/e)(x^x/y^y)^{1/(x-y)}$, and the classical arithmetic and geometric means, $A(x,y) = (x+y)/2$ and $G(x,y) = \sqrt{xy}$. In particular, we prove the following conjecture, which was published in 1986 [{\it H. Alzer}, Arch. Math. 47, 422-426 (1986; Zbl 0585.26014)]. If $M_r(x,y) = (x^r/2+y^r/2)^{1/r}$ ($r\neq 0$) denotes the power mean of order $r$, then $$M_c(x,y) <\frac 12(L(x,y)+I(x,y)) \qquad (x,y>0, x\neq y)$$ with the best possible parameter $c=(\log 2)/(1+\log 2)$.

##### MSC:
 26D15 Inequalities for sums, series and integrals of real functions 26E60 Means
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