In this article, we prove that the double inequalityαP(a, b) +(1- α)Q(a, b) M(a, b) βP(a, b) +(1- β)Q(a, b)holds for any a, b 0 with a = b if and only if α≥ 1/2 and β≤ [π(√2 log(1 +√2)-1)]/[(√2π- 2) log(1 +√2)] = 0.3595, where M(a, b), Q(a, b), and P(a, b) are the NeumanS′andor, quadratic, and first Seiffert means of a and b, respectively.
In this article, we prove that the double inequality P(a, b) + (1 - )Q(a, b) 0 with a 6= b if and only if ≥ 1/2 and ≤ [ (√ 2 log(1 +√ 2) - 1)]/[(√ 2 -2) log(1+√ 2)] = 0.3595 · · · , where M(a, b), Q(a, b), and P(a, b) are the Neuman- S′andor, quadratic, and first Seiffert means of a and b, respectively.