该文证明了双向不等式αQ(a,b)+(1-α)H(a,b)〈T(a,b)〈βQ(a,b)+(1-β)H(a,b)和λ/H(a,b)+(1-λ)/Q(a,b)〈1/T(a,b)〈μ/H(a,b)+(1-μ)/Q(a,b)对所有a,b〉0且a≠b成立的充分和必要条件是α≤5/6,β≥2√2π,λ≤0和μ≥1/6.其中Q(a,b)=√(a^2+b^2)/2,H(a,b)=2ab/(a+b)和T(a,b)=2/π∫0^π/2√a^2cos^2θ+b^2sin^2θdθ分别表示正数a和b的二次平均,调和平均和Toader平均.
We prove that the double inequalities αQ(a,b)+(1-α)H(a,b)〈T(a,b)〈βQ(a,b)+(1-β)H(a,b) and λ/H(a,b)+(1-λ)/Q(a,b)〈1/T(a,b)〈μ/H(a,b)+(1-μ)/Q(a,b) hold for all a,b〉0 with a≠b if and only if α≤5/6,β≥2√2π,λ≤0 and μ≥1/6.Here,Q(a,b)=√(a^2+b^2)/2,H(a,b)=2ab/(a+b) and T(a,b)=2/π∫0^π/2√a^2cos^2θ+b^2sin^2θdθ denote the quadratic,harmonic and Toader means of two positive numbers a and b,respectively.