Sharp One-Parameter Mean Bounds for Yang Mean

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Feb 9, 2016 - Wei-Mao Qian,1 Yu-Ming Chu,2 and Xiao-Hui Zhang2. 1School of Distance Education, Huzhou Broadcast and TV University, Huzhou 313000,Β ...
Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2016, Article ID 1579468, 5 pages http://dx.doi.org/10.1155/2016/1579468

Research Article Sharp One-Parameter Mean Bounds for Yang Mean Wei-Mao Qian,1 Yu-Ming Chu,2 and Xiao-Hui Zhang2 1

School of Distance Education, Huzhou Broadcast and TV University, Huzhou 313000, China School of Mathematics and Computation Sciences, Hunan City University, Yiyang 413000, China

2

Correspondence should be addressed to Yu-Ming Chu; [email protected] Received 19 July 2015; Accepted 9 February 2016 Academic Editor: Yann Favennec Copyright Β© 2016 Wei-Mao Qian et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We prove that the double inequality 𝐽𝛼 (π‘Ž, 𝑏) < π‘ˆ(π‘Ž, 𝑏) < 𝐽𝛽 (π‘Ž, 𝑏) holds for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 if and only if 𝛼 ≀ √2/(πœ‹ βˆ’ √2) = 0.8187 β‹… β‹… β‹… and 𝛽 β‰₯ 3/2, where π‘ˆ(π‘Ž, 𝑏) = (π‘Žβˆ’π‘)/[√2 arctan((π‘Žβˆ’π‘)/√2π‘Žπ‘)], and 𝐽𝑝 (π‘Ž, 𝑏) = 𝑝(π‘Žπ‘+1 βˆ’π‘π‘+1 )/[(𝑝+1)(π‘Žπ‘ βˆ’π‘π‘ )] (𝑝 =ΜΈ 0, βˆ’1), 𝐽0 (π‘Ž, 𝑏) = (π‘Ž βˆ’ 𝑏)/(log π‘Ž βˆ’ log 𝑏), and π½βˆ’1 (π‘Ž, 𝑏) = π‘Žπ‘(log π‘Ž βˆ’ log 𝑏)/(π‘Ž βˆ’ 𝑏) are the Yang and 𝑝th one-parameter means of π‘Ž and 𝑏, respectively.

1. Introduction Let 𝑝 ∈ R and π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏. Then the 𝑝th oneparameter mean 𝐽𝑝 (π‘Ž, 𝑏), 𝑝th power mean 𝑀𝑝 (π‘Ž, 𝑏), harmonic mean 𝐻(π‘Ž, 𝑏), geometric mean 𝐺(π‘Ž, 𝑏), logarithmic mean 𝐿(π‘Ž, 𝑏), first Seiffert mean 𝑃(π‘Ž, 𝑏), identric mean 𝐼(π‘Ž, 𝑏), arithmetic mean 𝐴(π‘Ž, 𝑏), Yang mean π‘ˆ(π‘Ž, 𝑏), second Seiffert mean 𝑇(π‘Ž, 𝑏), and quadratic mean 𝑄(π‘Ž, 𝑏) are, respectively, defined by 𝑝+1

𝑝+1

𝑝 (π‘Ž βˆ’ 𝑏 ) { { , 𝑝 =ΜΈ 0, βˆ’1, { { { (𝑝 + 1) (π‘Žπ‘ βˆ’ 𝑏𝑝 ) { { { { { π‘Žβˆ’π‘ 𝐽𝑝 (π‘Ž, 𝑏) = { , 𝑝 = 0, { { log π‘Ž βˆ’ log 𝑏 { { { { { { { π‘Žπ‘ (log π‘Ž βˆ’ log 𝑏) , 𝑝 = βˆ’1, { π‘Žβˆ’π‘ 𝑀𝑝 (π‘Ž, 𝑏) = [

𝑝

𝑝

π‘Ž +𝑏 ] 2

𝑀0 (π‘Ž, 𝑏) = βˆšπ‘Žπ‘, 2π‘Žπ‘ 𝐻 (π‘Ž, 𝑏) = , π‘Ž+𝑏 𝐺 (π‘Ž, 𝑏) = βˆšπ‘Žπ‘,

1/𝑝

(𝑝 =ΜΈ 0) ,

𝐿 (π‘Ž, 𝑏) =

π‘βˆ’π‘Ž , log 𝑏 βˆ’ log π‘Ž

𝑃 (π‘Ž, 𝑏) =

π‘Žβˆ’π‘ , 2 arcsin ((π‘Ž βˆ’ 𝑏) / (π‘Ž + 𝑏))

𝐼 (π‘Ž, 𝑏) =

1 𝑏𝑏 ( ) 𝑒 π‘Žπ‘Ž

𝐴 (π‘Ž, 𝑏) =

π‘Ž+𝑏 , 2

π‘ˆ (π‘Ž, 𝑏) =

π‘Žβˆ’π‘ , √2 arctan ((π‘Ž βˆ’ 𝑏) /√2π‘Žπ‘)

𝑇 (π‘Ž, 𝑏) =

π‘Žβˆ’π‘ , 2 arctan ((π‘Ž βˆ’ 𝑏) / (π‘Ž + 𝑏))

1/(π‘βˆ’π‘Ž)

𝑄 (π‘Ž, 𝑏) = √

,

π‘Ž2 + 𝑏2 . 2 (1)

It is well known that both the means 𝐽𝑝 (π‘Ž, 𝑏) and 𝑀𝑝 (π‘Ž, 𝑏) are continuous and strictly increasing with respect to 𝑝 ∈ R for fixed π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏. Recently, the one-parameter mean 𝐽𝑝 (π‘Ž, 𝑏) and Yang mean π‘ˆ(π‘Ž, 𝑏) have attracted the attention of many researchers.

2

Mathematical Problems in Engineering Alzer [1] proved that the inequalities

In [12, 13], the authors proved that the double inequalities

𝐺 (π‘Ž, 𝑏) < βˆšπ½π‘ (π‘Ž, 𝑏) π½βˆ’π‘ (π‘Ž, 𝑏) < 𝐿 (π‘Ž, 𝑏)
0 with π‘Ž =ΜΈ 𝑏 and 𝑝 =ΜΈ 0. In [2, 3], the authors discussed the monotonicity and logarithmic convexity properties of the one-parameter mean 𝐽𝑝 (π‘Ž, 𝑏). In [4, 5], the authors proved that the double inequalities 𝐽𝑝1 (π‘Ž, 𝑏) < 𝛼𝐴 (π‘Ž, 𝑏) + (1 βˆ’ 𝛼) 𝐿 (π‘Ž, 𝑏) < π½π‘ž1 (π‘Ž, 𝑏) 𝐽𝑝2 (π‘Ž, 𝑏) < 𝛼𝐴 (π‘Ž, 𝑏) + (1 βˆ’ 𝛼) 𝐻 (π‘Ž, 𝑏) < π½π‘ž2 (π‘Ž, 𝑏) ,

(3)

hold for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 and 𝛼 ∈ (0, 1) if and only if 𝑝1 ≀ 𝛼/(2 βˆ’ 𝛼), π‘ž1 β‰₯ 𝛼, 𝑝2 ≀ 3𝛼 βˆ’ 2, and π‘ž2 β‰₯ 𝛼/(2 βˆ’ 𝛼). Xia et al. [6] proved that the double inequality 𝐽(3π›Όβˆ’1)/2 (π‘Ž, 𝑏) < 𝛼𝐴 (π‘Ž, 𝑏) + (1 βˆ’ 𝛼) 𝐺 (π‘Ž, 𝑏)

(4)

< 𝐽𝛼/(2βˆ’π›Ό) (π‘Ž, 𝑏)

holds for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 if 𝛼 ∈ (0, 2/3), and inequality (4) is reversed if 𝛼 ∈ (2/3, 1). Gao and Niu [7] presented the best possible parameters 𝑝 and π‘ž such that the double inequality 𝐽𝑝 (π‘Ž, 𝑏) < 𝐴𝛼 (π‘Ž, 𝑏)𝐺𝛽 (π‘Ž, 𝑏)𝐻1βˆ’π›Όβˆ’π›½ (π‘Ž, 𝑏) < π½π‘ž (π‘Ž, 𝑏) holds for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 and 𝛼 + 𝛽 ∈ (0, 1). In [8, 9], the authors proved that the double inequalities π½πœ† 1 (π‘Ž, 𝑏) < 𝑇 (π‘Ž, 𝑏) < π½πœ‡1 (π‘Ž, 𝑏) ,

(5)

π½πœ† 2 (π‘Ž, 𝑏) < 𝐼 (π‘Ž, 𝑏) < π½πœ‡2 (π‘Ž, 𝑏)

hold for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 if and only if πœ† 1 ≀ 2/(2 βˆ’ πœ‹), πœ‡1 β‰₯ 2, πœ† 2 ≀ 1/2, and πœ‡2 β‰₯ 1/(𝑒 βˆ’ 1). Xia et al. [10] found that 𝑀(1+2𝑝)/3 (π‘Ž, 𝑏) is the best possible lower power mean bound for the one-parameter mean 𝐽𝑝 (π‘Ž, 𝑏) if 𝑝 ∈ (βˆ’2, βˆ’1/2) βˆͺ (1, ∞) and 𝑀(1+2𝑝)/3 (π‘Ž, 𝑏) is the best possible upper power mean bound for the oneparameter mean 𝐽𝑝 (π‘Ž, 𝑏) if 𝑝 ∈ (βˆ’βˆž, βˆ’2) βˆͺ (βˆ’1/2, 1). For all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏, Yang [11] provided the bounds for the Yang mean π‘ˆ(π‘Ž, 𝑏) in terms of other bivariate means as follows: 𝑃 (π‘Ž, 𝑏) < π‘ˆ (π‘Ž, 𝑏) < 𝑇 (π‘Ž, 𝑏) ,

< 𝑄2/3 (π‘Ž, 𝑏) [

𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) ] 2

2 𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) π‘ž 1 π‘ž 0 with π‘Ž =ΜΈ 𝑏.

2. Main Result In order to prove our main result we need a lemma, which we present in this section. Lemma 1. Let 𝑝 ∈ R, and

βˆ’ (𝑝 + 1) π‘₯4𝑝+1 βˆ’ 𝑝 (𝑝 + 1) π‘₯2𝑝+7

2𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) 1/2 ] < π‘ˆ (π‘Ž, 𝑏) 3 1/3

1/𝑝

𝑓 (π‘₯, 𝑝) = 𝑝π‘₯4𝑝+6 βˆ’ (𝑝 + 1) π‘₯4𝑝+5 + 𝑝π‘₯4𝑝+4

𝑃 (π‘Ž, 𝑏) 𝑄 (π‘Ž, 𝑏) 𝐺 (π‘Ž, 𝑏) 𝑇 (π‘Ž, 𝑏) < π‘ˆ (π‘Ž, 𝑏) < , 𝐴 (π‘Ž, 𝑏) 𝐴 (π‘Ž, 𝑏) 𝑄1/2 (π‘Ž, 𝑏) [

2 𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) 𝑝 1 𝑝 [ ( ) + 𝑄 (π‘Ž, 𝑏)] 3 2 3

2

+ 2 (𝑝 + 1) π‘₯2𝑝+5 βˆ’ 2𝑝π‘₯2𝑝+4 (6)

,

βˆ’ 2𝑝 (𝑝 + 1) π‘₯2𝑝+3 βˆ’ 2𝑝π‘₯2𝑝+2 2

+ 2 (𝑝 + 1) π‘₯2𝑝+1 βˆ’ 𝑝 (𝑝 + 1) π‘₯2π‘βˆ’1

𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) < π‘ˆ (π‘Ž, 𝑏) 2

βˆ’ (𝑝 + 1) π‘₯5 + 𝑝π‘₯2 βˆ’ (𝑝 + 1) π‘₯ + 𝑝. 2

2 𝐺 (π‘Ž, 𝑏) + 𝑄 (π‘Ž, 𝑏) 1/2 1 1/2 ) + 𝑄 (π‘Ž, 𝑏)] . 0 for all π‘₯ ∈ (1, ∞);

(9)

Mathematical Problems in Engineering

3

(2) if 𝑝 = √2/(πœ‹ βˆ’ √2) = 0.8187 β‹… β‹… β‹… , then there exists πœ† ∈ (1, ∞) such that 𝑓(π‘₯, 𝑝) < 0 for π‘₯ ∈ (1, πœ†) and 𝑓(π‘₯, 𝑝) > 0 for π‘₯ ∈ (πœ†, ∞). Proof. For part (1), if 𝑝 = 3/2, then (9) becomes 𝑓 (π‘₯, 𝑝) =

1 (π‘₯ βˆ’ 1)6 (π‘₯2 + 2π‘₯ + 2) (2π‘₯2 + 2π‘₯ + 1) 4

lim 𝑓8 (π‘₯, 𝑝) = (𝑝 + 1) (2560𝑝5 + 6336𝑝4 + 14176𝑝3

π‘₯β†’1

+ 11028𝑝2 βˆ’ 12680𝑝 βˆ’ 22005) < 0, lim 𝑓 π‘₯β†’+∞ 8

(π‘₯, 𝑝) = +∞,

(21)

(22)

lim 𝑓9 (π‘₯, 𝑝) = 6 (512𝑝6 + 1184𝑝5 + 4064𝑝4

π‘₯β†’1

(10)

β‹… (3π‘₯2 + 4π‘₯ + 3) .

+ 6372𝑝3 + 4068𝑝2 βˆ’ 3495𝑝 βˆ’ 5775) = 15.2085

(23)

β‹… β‹… β‹… > 0,

Therefore, part (1) follows from (10). For part (2), let 𝑝 = √2/(πœ‹ βˆ’ √2), 𝑓1 (π‘₯, 𝑝) = πœ•π‘“(π‘₯, 𝑝)/πœ•π‘₯, 𝑓2 (π‘₯, 𝑝) = (1/2)(πœ•π‘“1 (π‘₯, 𝑝)/πœ•π‘₯), 𝑓3 (π‘₯, 𝑝) = (1/(𝑝 + 1)π‘₯2 )(πœ•π‘“2 (π‘₯, 𝑝)/πœ•π‘₯), 𝑓4 (π‘₯, 𝑝) = (π‘₯7βˆ’2𝑝 /2𝑝)(πœ•π‘“3 (π‘₯, 𝑝)/πœ•π‘₯), 𝑓5 (π‘₯, 𝑝) = (1/2π‘₯)(πœ•π‘“4 (π‘₯, 𝑝)/πœ•π‘₯), 𝑓6 (π‘₯, 𝑝) = πœ•π‘“5 (π‘₯, 𝑝)/πœ•π‘₯, 𝑓7 (π‘₯, 𝑝) = (1/2)(πœ•π‘“6 (π‘₯, 𝑝)/πœ•π‘₯), 𝑓8 (π‘₯, 𝑝) = πœ•π‘“7 (π‘₯, 𝑝)/πœ•π‘₯, 𝑓9 (π‘₯, 𝑝) = (1/2(𝑝+1))(πœ•π‘“8 (π‘₯, 𝑝)/πœ•π‘₯), and 𝑓10 (π‘₯, 𝑝) = πœ•π‘“9 (π‘₯, 𝑝)/πœ•π‘₯. Then elaborated computations lead to

2

𝑓10 (π‘₯, 𝑝) = (𝑝 + 2) (2𝑝 + 1) (2𝑝 + 3) (2𝑝 + 5) (2𝑝 + 7) (4𝑝 + 1) (4𝑝 + 5) π‘₯2𝑝 βˆ’ 8𝑝 (𝑝 + 1) (𝑝 + 2) (𝑝 + 3) (2𝑝 + 1) (2𝑝 + 3) (4𝑝 + 3) (4𝑝 + 5) π‘₯2π‘βˆ’1 2

+ 𝑝 (2𝑝 βˆ’ 1) (2𝑝 + 1) (2𝑝 + 3) (2𝑝 + 5) (4𝑝 βˆ’ 1)

(24)

2

β‹… (4𝑝 + 3) π‘₯2π‘βˆ’2 βˆ’ 8𝑝 (𝑝 βˆ’ 1) (𝑝 βˆ’ 2) (2𝑝 βˆ’ 1) (2𝑝 lim 𝑓 (π‘₯, 𝑝) = 0,

π‘₯β†’1

(11)

lim 𝑓 (π‘₯, 𝑝) = +∞,

+ 7) π‘₯.

π‘₯β†’+∞

lim 𝑓1 (π‘₯, 𝑝) = 0,

Note that

π‘₯β†’1

lim 𝑓 π‘₯β†’+∞ 1

(12)

(π‘₯, 𝑝) = +∞,

π‘₯β†’1

(13)

(π‘₯, 𝑝) = +∞,

lim 𝑓3 (π‘₯, 𝑝) = 0,

(14)

(π‘₯, 𝑝) = +∞,

3 lim 𝑓4 (π‘₯, 𝑝) = βˆ’48 (𝑝 + 1) ( βˆ’ 𝑝) < 0, 2

(15)

π‘₯β†’+∞

3 lim 𝑓5 (π‘₯, 𝑝) = βˆ’192 (𝑝 + 1) ( βˆ’ 𝑝) < 0, π‘₯β†’1 2

2

(26)

β‹… π‘₯2π‘βˆ’2 = (1536𝑝7 + 15040𝑝6 + 59440𝑝5

(17)

βˆ’ 963) < 0,

(18)

+ 122280𝑝4 + 137144𝑝3 + 61850𝑝2 βˆ’ 49845𝑝 βˆ’ 72450) π‘₯ + 𝑝 (2𝑝 βˆ’ 1) (4𝑝 βˆ’ 1) (704𝑝4 + 136𝑝3 + 1120𝑝2 + 248𝑝 βˆ’ 3) π‘₯2π‘βˆ’2 > 0,

lim 𝑓7 (π‘₯, 𝑝) = (𝑝 + 1) (1024𝑝4 + 2096𝑝3 + 1844𝑝2

(19)

βˆ’ 2876𝑝 βˆ’ 5193) < 0, (π‘₯, 𝑝) = +∞,

β‹… (2𝑝 + 1) (2𝑝 + 3) (2𝑝 + 5) (4𝑝 βˆ’ 1) (4𝑝 + 3) βˆ’ 8𝑝 (𝑝 βˆ’ 1) (𝑝 βˆ’ 2) (2𝑝 βˆ’ 1) (2𝑝 βˆ’ 3) (16𝑝2 βˆ’ 1)]

lim 𝑓6 (π‘₯, 𝑝) = 2 (𝑝 + 1) (368𝑝3 + 332𝑝2 βˆ’ 484𝑝

(π‘₯, 𝑝) = +∞,

β‹… (𝑝 + 3) (2𝑝 + 1) (2𝑝 + 3) (4𝑝 + 3) (4𝑝 + 5)

2

(16)

(π‘₯, 𝑝) = +∞,

π‘₯β†’1

lim 𝑓 π‘₯β†’+∞ 7

2

βˆ’ 720 (𝑝 + 3) (2𝑝 + 5) (2𝑝 + 7)] π‘₯ + [𝑝 (2𝑝 βˆ’ 1)

2

π‘₯β†’1

It follows from (24) and (25) that

β‹… (2𝑝 + 7) (4𝑝 + 1) (4𝑝 + 5) βˆ’ 8𝑝 (𝑝 + 1) (𝑝 + 2)

lim 𝑓4 (π‘₯, 𝑝) = +∞,

lim 𝑓 π‘₯β†’+∞ 6

(25)

𝑓10 (π‘₯, 𝑝) > [(𝑝 + 2) (2𝑝 + 1) (2𝑝 + 3) (2𝑝 + 5)

π‘₯β†’1

lim 𝑓 π‘₯β†’+∞ 5

+ 137144𝑝3 + 61850𝑝2 βˆ’ 49845𝑝 βˆ’ 72450 = 85165.4405 β‹… β‹… β‹… > 0.

π‘₯β†’1

lim 𝑓 π‘₯β†’+∞ 3

2𝑝 > 1 > 2𝑝 βˆ’ 1 > 0 > 2𝑝 βˆ’ 2 > 2𝑝 βˆ’ 5, 1536𝑝7 + 15040𝑝6 + 59440𝑝5 + 122280𝑝4

lim 𝑓2 (π‘₯, 𝑝) = 0,

lim 𝑓 π‘₯β†’+∞ 2

βˆ’ 3) (16𝑝2 βˆ’ 1) π‘₯2π‘βˆ’5 βˆ’ 720 (𝑝 + 3) (2𝑝 + 5) (2𝑝

(20)

for π‘₯ ∈ (1, ∞). From (23) and (26) we clearly see that 𝑓8 (π‘₯, 𝑝) is strictly increasing with respect to π‘₯ on the interval (1, ∞). Then (21) and (22) lead to the conclusion that there exists πœ† 1 > 1 such

4

Mathematical Problems in Engineering

that the function π‘₯ β†’ 𝑓7 (π‘₯, 𝑝) is strictly decreasing on (1, πœ† 1 ] and strictly increasing on [πœ† 1 , ∞). It follows from (19) and (20) together with the piecewise monotonicity of the function π‘₯ β†’ 𝑓7 (π‘₯, 𝑝) that there exists πœ† 2 > 1 such that the function π‘₯ β†’ 𝑓6 (π‘₯, 𝑝) is strictly decreasing on (1, πœ† 2 ] and strictly increasing on [πœ† 2 , ∞). Making use of (13)–(18) and the same method as the above we know that there exists πœ† 𝑖 > 1 (𝑖 = 3, 4, 5, 6, 7) such that the function π‘₯ β†’ 𝑓8βˆ’π‘– (π‘₯, 𝑝) is strictly decreasing on (1, πœ† 𝑖 ] and strictly increasing on [πœ† 𝑖 , ∞). It follows from (12) and the piecewise monotonicity of the function π‘₯ β†’ 𝑓1 (π‘₯, 𝑝) that there exists πœ†βˆ— > 1 such that the function π‘₯ β†’ 𝑓(π‘₯, 𝑝) is strictly decreasing on (1, πœ†βˆ— ] and strictly increasing on [πœ†βˆ— , ∞). Therefore, part (2) follows easily from (11) and the piecewise monotonicity of the function π‘₯ β†’ 𝑓(π‘₯, 𝑝).

𝐽𝛼 (π‘Ž, 𝑏) < π‘ˆ (π‘Ž, 𝑏) < 𝐽𝛽 (π‘Ž, 𝑏)

(27)

holds for all π‘Ž, 𝑏 > 0 with π‘Ž =ΜΈ 𝑏 if and only if 𝛼 ≀ √2/(πœ‹βˆ’βˆš2) = 0.8187 β‹… β‹… β‹… and 𝛽 β‰₯ 3/2. Proof. Since π‘ˆ(π‘Ž, 𝑏) and 𝐽𝑝 (π‘Ž, 𝑏) are symmetric and homogeneous of degree one, without loss of generality, we assume that π‘Ž = π‘₯2 > 1 and 𝑏 = 1. Let 𝑝 ∈ R and 𝑝 =ΜΈ 0, βˆ’1. Then (1) lead to 2

𝐽𝑝 (π‘Ž, 𝑏) βˆ’ π‘ˆ (π‘Ž, 𝑏) = 𝐽𝑝 (π‘₯ , 1) βˆ’ π‘ˆ (π‘₯ , 1) =

Case 2 (𝑝 > √2/(πœ‹ βˆ’ √2)). Then (1) leads to lim

𝐽𝑝 (π‘₯, 1)

π‘₯β†’βˆž π‘ˆ (π‘₯, 1)

=

√2𝑝 πœ‹ > 1. 2 (𝑝 + 1)

(34)

Inequality (34) implies that there exists large enough 𝑋 = 𝑋(𝑝) > 1 such that π‘ˆ(π‘Ž, 𝑏) < 𝐽𝑝 (π‘Ž, 𝑏) for all π‘Ž, 𝑏 > 0 with π‘Ž/𝑏 ∈ (0, 1/𝑋) βˆͺ (𝑋, ∞). Case 3 (𝑝 = 3/2). Then from Lemma 1(1) and (31) we know that the function π‘₯ β†’ 𝐹(π‘₯, 𝑝) is strictly increasing on the interval (1, ∞). Therefore, π‘ˆ (π‘Ž, 𝑏) < 𝐽3/2 (π‘Ž, 𝑏)

(35)

follows from (28) and (30) together with the monotonicity of the function π‘₯ β†’ 𝐹(π‘₯, 𝑝).

Theorem 2. The double inequality

2

follows easily from (28), (30), and (32) together with the piecewise monotonicity of the function π‘₯ β†’ 𝐹(π‘₯, 𝑝).

𝑝 (π‘₯2𝑝+2 βˆ’ 1) (𝑝 + 1) (π‘₯2𝑝 βˆ’ 1) arctan ((π‘₯2 βˆ’ 1) /√2π‘₯)

𝐹 (π‘₯, 𝑝) ,

(28)

Case 4 (0 < 𝑝 < 3/2). Let π‘₯ > 0 and π‘₯ β†’ 0; then making use of Taylor expansion we get π‘ˆ (1, 1 + π‘₯) βˆ’ 𝐽𝑝 (1, 1 + π‘₯) =

π‘₯ √2 arctan (π‘₯/√2 (1 + π‘₯)) βˆ’

𝑝 [1 βˆ’ (1 + π‘₯)𝑝+1 ] (𝑝 + 1) [1 βˆ’ (1 + π‘₯)𝑝 ]

=

(36) 3 βˆ’ 2𝑝 2 π‘₯ + π‘œ (π‘₯2 ) . 24

Equation (36) implies that there exists small enough 𝛿 > 0 such that π‘ˆ(1, 1 + π‘₯) > 𝐽𝑝 (1, 1 + π‘₯) for all π‘₯ ∈ (0, 𝛿).

Conflict of Interests

where 𝐹 (π‘₯, 𝑝) = arctan ( βˆ’

The authors declare that there is no conflict of interests regarding the publication of this paper.

π‘₯2 βˆ’ 1 ) √2π‘₯

(𝑝 + 1) (π‘₯2 βˆ’ 1) (π‘₯2𝑝 βˆ’ 1) √2𝑝 (π‘₯2𝑝+2 βˆ’ 1)

(29) ,

lim 𝐹 (π‘₯, 𝑝) = 0,

(30)

π‘₯β†’1

√2 πœ•πΉ (π‘₯, 𝑝) 𝑓 (π‘₯, 𝑝) , = 2 πœ•π‘₯ 𝑝 (π‘₯4 + 1) (π‘₯2𝑝+2 βˆ’ 1)

(31)

where 𝑓(π‘₯, 𝑝) is defined by (9). We divide the proof into four cases. Case 1 (𝑝 = √2/(πœ‹ βˆ’ √2)). Then it follows from Lemma 1(2), (29), and (31) that there exists πœ† > 1 such that the function π‘₯ β†’ 𝐹(π‘₯, 𝑝) is strictly decreasing on (1, πœ†] and strictly increasing on [πœ†, ∞), and lim 𝐹 (π‘₯, 𝑝) = 0.

(32)

𝐽√2/(πœ‹βˆ’βˆš2) (π‘Ž, 𝑏) < π‘ˆ (π‘Ž, 𝑏)

(33)

π‘₯β†’βˆž

Therefore,

Acknowledgments The research was supported by the Natural Science Foundation of China under Grants 61374086, 11371125, and 11401191 and the Natural Science Foundation of Zhejiang Broadcast and TV University under Grant XKT-15G17.

References Β¨ [1] H. Alzer, Uber eine Einparametrige Familie von Mittelwerten, Die Bayerische Akademie der Wissenschaften, 1988. [2] W.-S. Cheung and F. Qi, β€œLogarithmic convexity of the oneparameter mean values,” Taiwanese Journal of Mathematics, vol. 11, no. 1, pp. 231–237, 2007. [3] F. Qi, P. Cerone, S. S. Dragomir, and H. M. Srivastava, β€œAlternative proofs for monotonic and logarithmically convex properties of one-parameter mean values,” Applied Mathematics and Computation, vol. 208, no. 1, pp. 129–133, 2009. [4] M.-K. Wang, Y.-F. Qiu, and Y.-M. Chu, β€œAn optimal double inequality among the oneparameter, arithmetic and harmonic means,” Revue d’Analyse NumΒ΄erique et de ThΒ΄eorie de l’Approximation, vol. 39, no. 2, pp. 169–175, 2010.

Mathematical Problems in Engineering [5] Z.-Y. He, M.-K. Wang, and Y.-M. Chu, β€œOptimal one-parameter mean bounds for the convex combination of arithmetic and logarithmic means,” Journal of Mathematical Inequalities, vol. 9, no. 3, pp. 699–707, 2015. [6] W.-F. Xia, S.-W. Hou, G.-D. Wang, and Y.-M. Chu, β€œOptimal one-parameter mean bounds for the convex combination of arithmetic and geometric means,” Journal of Applied Analysis, vol. 18, no. 2, pp. 197–207, 2012. [7] H.-Y. Gao and W.-J. Niu, β€œSharp inequalities related to oneparameter mean and Gini mean,” Journal of Mathematical Inequalities, vol. 6, no. 4, pp. 545–555, 2012. [8] H.-N. Hu, G.-Y. Tu, and Y.-M. Chu, β€œOptimal bounds for Seiffert mean in terms of one-parameter means,” Journal of Applied Mathematics, vol. 2012, Article ID 917120, 7 pages, 2012. [9] Y.-Q. Song, W.-F. Xia, X.-H. Shen, and Y.-M. Chu, β€œBounds for the identric mean in terms of one-parameter mean,” Applied Mathematical Sciences, vol. 7, no. 88, pp. 4375–4386, 2013. [10] W.-F. Xia, G.-D. Wang, Y.-M. Chu, and S.-W. Hou, β€œSharp inequalities between one-parameter and power means,” Advances in Mathematics, vol. 42, no. 5, pp. 713–722, 2013. [11] Z.-H. Yang, β€œThree families of two-parameter means constructed by trigonometric functions,” Journal of Inequalities and Applications, vol. 2013, article 541, 27 pages, 2013. [12] Z.-H. Yang, Y.-M. Chu, Y.-Q. Song, and Y.-M. Li, β€œA sharp double inequality for trigonometric functions and its applications,” Abstract and Applied Analysis, vol. 2014, Article ID 592085, 9 pages, 2014. [13] Z.-H. Yang, L.-M. Wu, and Y.-M. Chu, β€œOptimal power mean bounds for Yang mean,” Journal of Inequalities and Applications, vol. 2014, article 401, 10 pages, 2014. [14] S.-S. Zhou, W.-M. Qian, Y.-M. Chu, and X.-H. Zhang, β€œSharp power-type Heronian mean bounds for the SΒ΄andor and Yang means,” Journal of Inequalities and Applications, vol. 2015, article 159, 10 pages, 2015.

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