Available online at www.tjnsa.com J. Nonlinear Sci. Appl. 9 (2016), 139–148 Research Article Some inequalities of Hermite–Hadamard type for functions whose second derivatives are (α, m)-convex Ye Shuanga , Feng Qib,∗, Yan Wanga a College of Mathematics, Inner Mongolia University for Nationalities, Tongliao City, Inner Mongolia Autonomous Region, China. b Department of Mathematics, College of Science, Tianjin Polytechnic University, Tianjin City, 300160, China. Communicated by C. Park Abstract In the paper, the authors establish a new integral identity and by this identity with the Hölder integral inequality, discover some new Hermite–Hadamard type integral inequalities for functions whose second c derivatives are (α, m)-convex. 2016 All rights reserved. Keywords: Hermite–Hadamard type inequality, (α, m)-convex function, second derivative, Hölder integral inequality. 2010 MSC: 26D15, 26A51, 41A55. 1. Introduction It is common knowledge in mathematical analysis that a function f : I ⊆ R → R is said to be convex on an interval I if f (λx + (1 − λ)y) ≤ λf (x) + (1 − λ)f (y) for all x, y ∈ I and λ ∈ [0, 1]. Suppose that f : I ⊆ R → R is a convex function on an interval I such that a, b ∈ I and a < b. Then the well-known Hermite–Hadamard integral inequality reads that Z b f (a) + f (b) a+b 1 f ≤ f (x) d x ≤ . 2 b−a a 2 ∗ Corresponding author Email addresses: shuangye152300@sina.com (Ye Shuang), qifeng618@gmail.com, qifeng618@hotmail.com (Feng Qi), sella110@vip.qq.com (Yan Wang) Received 2015-06-25 Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 140 Definition 1.1 ([9]). For f : [0, b] → R and m ∈ (0, 1], if f (λx + m(1 − λ)y) ≤ λf (x) + m(1 − λ)f (y) is valid for all x, y ∈ [0, b] and λ ∈ [0, 1], then we say that f (x) is an m-convex function on [0, b]. Definition 1.2 ([5]). For f : [0, b] → R and (α, m) ∈ (0, 1]2 , if f (λx + m(1 − λ)y) ≤ λα f (x) + m 1 − λα f (y) is valid for all x, y ∈ [0, b] and λ ∈ [0, 1], then we say that f (x) is an (α, m)-convex function on [0, b]. For the above convex functions, we recite the following theorems. Theorem 1.3 ([2, Theorem 2.2]). Let f : I ◦ ⊆ R → R be a differentiable mapping and a, b ∈ I ◦ with a < b. If |f 0 (x)| is convex on [a, b], then Z b f (a) + f (b) (b − a) 0 1 f (x) d x ≤ − |f (a)| + |f 0 (b)| . 2 b−a a 8 Theorem 1.4 ([1, Theorem 2.2]). Let I ⊇ R0 = [0, ∞) be an open interval and let f : I → R be a differentiable function such that f 0 ∈ L[a, b] for 0 ≤ a < b < ∞. If |f 0 (x)|q is m-convex on [a, b] for some m ∈ (0, 1] and q ≥ 1, then 0 Z b a+b b−a 1 |f (a)|q + m|f 0 (b/m)|q 1/q m|f 0 (a/m)|q + |f 0 (b)|q 1/q f − f (x) d x≤ min , . 2 b−a a 4 2 2 Theorem 1.5 ([1, Theorem 3.1]). Let I ⊇ R0 be an open real interval and let f : I → R be a differentiable function on I such that f 0 ∈ L([a, b]) for 0 ≤ a < b < ∞. If |f 0 |q is (α, m)-convex on [a, b] for some given numbers m, α ∈ (0, 1] and q ≥ 1, then q 1/q Z b f (a) + f (b) b − a 1 1−1/q 1 b 0 q − f (x) d x ≤ × min v1 |f (a)| + v2 mf 0 , 2 b−a a 2 2 m q 1/q a 0 q v2 mf 0 + v |f (b)| , 1 m where 1 1 α+ α v1 = (α + 1)(α + 2) 2 and 2 1 α +α+2 1 v2 = − α . (α + 1)(α + 2) 2 2 In recent years, some other kinds of Hermite–Hadamard type inequalities were generated in, for example, [4, 7, 8, 10, 11, 12]. For more systematic information, please refer to monographs [3, 6] and related references therein. In this paper, we will establish a new integral identity and discover some new Hermite–Hadamard type integral inequalities for functions whose second derivatives are (α, m)-convex. 2. A lemma For establishing some new integral inequalities of Hermite–Hadamard type for functions whose second derivatives are (α, m)-convex, we need the following lemma. Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 141 Lemma 2.1. Let f : I ⊆ R → R be differentiable on I ◦ and a, b ∈ I with a < b. If f 00 ∈ L([a, b]), then Z b f (a) + f (b) 1 f (x) d x − 2 b−a a Z 1 2a + b (b − a)2 2 00 = (2 − t − t )f ta + (1 − t) dt 54 3 0 Z 1 2a + b a + 2b 2 00 (2 + t − t )f t + dt + (1 − t) 3 3 0 Z 1 a + 2b 2 00 (3t − t )f t + + (1 − t)b d t . 3 0 Proof. Integrating by part and changing the variable of definite integral yield Z 1 2a + b 2 00 (2 − t − t )f ta + (1 − t) dt 3 0 Z 1 2a + b 6 2a + b 3 =− + (1 + 2t)f 0 ta + (1 − t) dt f0 a−b 3 a−b 0 3 6 27 9 2a + b 0 2a + b =− f + f (a) − f a−b 3 (a − b)2 (a − b)2 3 Z 1 Z 1 18 2a + b 2a + b a + 2b 2 00 − f ta + (1 − t) dt (2 + t − t )f t + (1 − t) dt (a − b)2 0 3 3 3 0 6 2a + b 6 a + 2b = f0 − f0 a−b 3 a−b 3 Z 1 3 2a + b a + 2b 0 − (1 − 2t)f t + (1 − t) dt a−b 0 3 3 9 2a + b a + 2b 6 0 2a + b 0 a + 2b f −f + f +f = a−b 3 3 (a − b)2 3 3 Z 1 18 2a + b a + 2b − f t + (1 − t) dt (a − b)2 0 3 3 and Z 0 1 a + 2b (3t − t )f t + (1 − t)b d t 3 Z 1 3 a + 2b 6 0 a + 2b 0 (3 − 2t)f t = f − + (1 − t)b d t a−b 3 a−b 0 3 6 a + 2b 9 a + 2b 27 = f0 − f + f (b) 2 a−b 3 (a − b) 3 (a − b)2 Z 1 a + 2b 18 f t − + (1 − t)b d t. (a − b)2 0 3 2 00 Lemma 2.1 is thus proved. 3. Hermite–Hadamard type inequalities for (α, m)-convex functions Now we start out to establish some new Hermite–Hadamard type integral inequalities for functions whose second derivatives are (α, m)-convex. Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 142 Theorem 3.1. Let f : R0 → R be twice differentiable and f 00 ∈ L([a, b]) for 0 ≤ a < b. If |f 00 |q is an b (α, m)-convex function on 0, m for (α, m) ∈ (0, 1]2 and q ≥ 1, then Z b f (a) + f (b) 1 f (x) d x − 2 b−a a 1/q 1 (b − a)2 ≤ 324 (α + 1)(α + 2)(α + 3) ( 00 q 00 2a + b q 1/q 2 1−1/q × 7 6(3α + 7) f (a) + mα 7α + 42α + 59 f 3m 00 2a + b q 00 a + 2b q 1/q 2 2 1−1/q 6 2α + 11α + 13 f + 13 + mα 13α + 66α + 77 f 3 3m ) 00 a + 2b q 00 b q 1/q 1−1/q 2 2 +7 6 2α + 9α + 7 f . +mα 7α + 30α + 23 f 3 m b Proof. Because |f 00 |q is (α, m)-convex on 0, m , by Lemma 2.1 and the Hölder integral inequality, we have Z b f (a) + f (b) 1 f (x) d x − 2 b−a a Z 1 2a + b (b − a)2 2 00 (2 − t − t ) f ta + (1 − t) ≤ dt 54 3 0 Z 1 a + 2b 2a + b 2 00 + (1 − t) + (2 + t − t ) f t dt 3 3 0 Z 1 a + 2b 2 00 + (1 − t)b d t + (3t − t ) f t 3 0 Z 1 1−1/q 2 (b − a) 2 ≤ (2 − t − t ) d t 54 0 Z 1 1/q 2a + b q 2 00 (2 − t − t ) f ta + (1 − t) × dt 3 0 1/q Z 1 1−1/q Z 1 a + 2b q 2a + b 2 2 00 + (1 − t) + (2 + t − t ) d t (2 + t − t ) f t dt 3 3 0 0 q 1/q ) Z 1 1−1/q Z 1 a + 2b + (1 − t)b d t + (3t − t2 ) d t (3t − t2 ) f 00 t 3 0 0 q 1/q Z 1 q (b − a)2 7 1−1/q 2 α 00 α 00 2a + b ≤ (2 − t − t ) t f (a) + m(1 − t ) f dt 54 6 3m 0 1−1/q Z 1 q 1/q 13 2a + b q α 00 a + 2b f + (2 + t − t2 ) tα f 00 + m(1 − t ) dt 6 3 3m 0 1−1/q Z 1 q q 1/q ) 7 a + 2b b + m(1 − tα )f 00 + (3t − t2 ) tα f 00 dt 6 3 m 0 1/q (b − a)2 1 = 324 (α + 1)(α + 2)(α + 3) ( 00 q 00 2a + b q 1/q 1−1/q 2 × 7 6(3α + 7) f (a) + mα 7α + 42α + 59 f 3m Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 143 00 2a + b q 00 a + 2b q 1/q 2 + mα 13α + 66α + 77 f 6 2α + 11α + 13 f + 13 3 3m q 1/q ) q a + 2b +mα 7α2 + 30α + 23 f 00 b + 71−1/q 6 2α2 + 9α + 7 f 00 . 3 m 1−1/q 2 The proof of Theorem 3.1 is completed. Corollary 3.2. Under the conditions of Theorem 3.1, if α = m = 1, we have Z b f (a) + f (b) 1 f (x) d x − 2 b−a a " " q #1/q q 00 + f 13 f 00 2a+b 7(b − a)2 5|f 00 (a)|q + 9 f 00 2a+b 3 3 + ≤ 324 14 7 2 " # q + 5 |f 00 (b)|q 1/q 9 f 00 a+2b 3 + . 14 Corollary 3.3. Under the conditions of Theorem 3.1, if α = m = q = 1, we have " Z b + 22 f 00 f (a) + f (b) (b − a)2 5 |f 00 (a)| + 22 f 00 2a+b 1 3 f (x) d x ≤ − 2 b−a a 12 54 a+2b 3 a+2b 3 q #1/q # + 5 |f 00 (b)| . Theorem 3.4. Let differentiable and f 00 ∈ L([a, b]) for 0 ≤ a < b. If |f 00 |q is fb : R0 → R be twice 2 (α, m)-convex on 0, m for (α, m) ∈ (0, 1] and q > 1, then Z b f (a) + f (b) 1 − f (x) d x 2 b−a a 1/p 1/q 1 1 (b − a)2 ≤ 54 (p + 1)(p + 2) 2(α + 1)(α + 2) 00 2a + b q 1/q 1/p 00 q p+2 p+1 × 3 − 2 (p + 4) 2 f (a) + mα(α + 3) f 3m 00 2a + b q 00 a + 2b q 1/q 1/p p+1 + 2 (p + 4) − 2p − 5 2(2α + 3) f + mα(3α + 5) f 3 3m q 1/q ) 00 a + 2b q 1/p p+2 p+1 + mα(α + 1) f 00 b + 3 − 2 (p + 4) 2(α + 1) f , 3 m (3.1) where 1 p + 1 q = 1. Proof. By Lemma 2.1 and the Hölder integral inequality, we have Z b f (a) + f (b) 1 − f (x) d x 2 b−a a Z 1 00 (b − a)2 2a + b ≤ (1 − t) (2 + t) f ta + (1 − t) dt 54 3 0 Z 1 00 2a + b a + 2b + (1 + t)(2 − t) f t + (1 − t) dt 3 3 0 Z 1 00 a + 2b + t(3 − t) f t + (1 − t)b d t 3 0 Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 Z 1 1/p Z 1 1/q 00 (b − a)2 2a + b q p ≤ (1 − t)(2 + t) d t (1 − t) f ta + (1 − t) dt 54 3 0 0 1/q Z 1 1/p Z 1 00 2a + b a + 2b q p + (1 − t) + (1 + t)(2 − t) d t (1 + t) f t dt 3 3 0 0 Z 1 1/p Z 1 q 1/q ) 00 a + 2b p + t(3 − t) d t t f t + (1 − t)b d t , 3 0 0 144 (3.2) where Z 1 2p+1 (p + 4) − 2p − 5 3p+2 − 2p+1 (p + 4) (1 + t)(2 − t)p d t = , , (p + 1)(p + 2) (p + 1)(p + 2) 0 0 (3.3) Z 1 3p+2 − 2p+1 (p + 4) p t(3 − t) d t = . (p + 1)(p + 2) 0 b Using the (α, m)-convexity of |f 00 |q on 0, m , we obtain q q Z 1 Z 1 00 q 00 2a + b α α dt ≤ f (a) + m(1 − t ) f 00 2a + b d t (1 − t) f ta + (1 − t) (1 − t) t 3 3m 0 0 00 q 00 2a + b q 1 , 2 f (a) + mα(α + 3) f = 2(α + 1)(α + 2) 3m Z Z 1 0 1 (1 − t)(2 + t)p d t = q Z 00 a + 2b t f t + (1 − t)b d t ≤ 3 q q b α 00 a + 2b α 00 t t f + m(1 − t ) f dt 3 m 0 q q 00 a + 2b 1 b 2(α + 1) f + mα(α + 1) f 00 , = 2(α + 1)(α + 2) 3 m 1 and Z 0 1 00 2a + b a + 2b q + (1 − t) (1 + t) f t dt 3 3 q Z 1 00 a + 2b q α 00 2a + b α dt (1 + t) t f ≤ + m(1 − t ) × f 3 3m 0 q 00 2a + b q 1 + mα(3α + 5) f 00 a + 2b ; 2(2α + 3) f = 2(α + 1)(α + 2) 3 3m Substituting the equalities in (3.3) into the above inequalities and the inequality (3.2) yields the inequality (3.1). The proof of Theorem 3.4 is complete. Corollary 3.5. Under the conditions of Theorem 3.4, if α = m = 1, we have 1/p 1/q Z b f (a) + f (b) (b − a)2 1 1 1 − f (x) d x ≤ 2 b−a a 54 (p + 1)(p + 2) 6 ( 00 2a + b q 1/q 1/p 00 q p+2 p+1 f (a) + 2 f × 3 − 2 (p + 4) 3 + 2 p+1 (p + 4) − 2p − 5 + 3p+2 − 2p+1 (p + 4) q 1/q 00 2a + b q + 4 f 00 a + 2b 5 f 3 3 ) 00 a + 2b q 00 q 1/q 2 f . + f (b) 3 1/p 1/p Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 145 Theorem 3.6. Let f : R0 → R be twice differentiable and f 00 ∈ L([a, b]) for 0 ≤ a < b. If |f 00 |q is an b (α, m)-convex function on 0, m for (α, m) ∈ (0, 1]2 , q > 1, and 0 < r ≤ q, then Z b f (a) + f (b) 1 − f (x) d x 2 b−a a ( 1−1/q q (q − 1)(7q − 2r − 5) (b − a)2 3α + 2r + 5 ≤ × B(α + 1, r + 1) f 00 (a) 54 (2q − r − 1)(3q − r − 2) α+r+2 2r + 5 3α + 2r + 5 +m − B(α + 1, r + 1) (r + 1)(r + 2) α+r+2 1−1/q p+1 00 2a + b q 1/q 00 2a + b q α+3 2 (p + 4) − 2p − 5 × f f + 3m (p + 1)(p + 2) (α + 1)(α + 2) 3 q 1/q 1−1/q 00 a + 2b α(3α + 7) (q − 1)(7q − 2r − 5) f +m + 2(α + 1)(α + 2) 3m (2q − r − 1)(3q − r − 2) q 2α + 2r + 5 f 00 a + 2b × (α + r + 1)(α + r + 2) 3 q 1/q ) 00 b 2α + 2r + 5 2r + 5 f − , + m (r + 1)(r + 2) (α + r + 1)(α + r + 2) m where 1 p + 1 q (3.4) = 1 and B(α, β) denotes the well-known Beta function which may be defined by Z B(α, β) = 1 tα−1 (1 − t)β−1 d t, α, β > 0. 0 Proof. From Lemma 2.1 and the Hölder integral inequality, we have Z b 1 f (a) + f (b) − f (x) d x | 2 b−a a Z 1 2 00 (b − a) 2a + b ≤ (1 − t) (2 + t) f ta + (1 − t) dt 54 3 0 Z 1 00 2a + b a + 2b + (1 − t) + (1 + t)(2 − t) f t dt 3 3 0 Z 1 00 a + 2b + t(3 − t) f t + (1 − t)b d t (3.5) 3 0 Z 1 1/p Z 1 1/q q−r (b − a)2 2a + b q ≤ (1 − t) q−1 (2 + t) d t d t (1 − t)r (2 + t) f 00 ta + (1 − t) 54 3 0 0 Z 1 1/p Z 1 1/q 00 2a + b a + 2b q p (1 + t) (2 − t) d t (2 − t) f t + + (1 − t) dt 3 3 0 0 Z 1 1/p Z 1 q 1/q ) 00 a + 2b q−r r + t q−1 (3 − t) d t . t (3 − t) f t + (1 − t)b d t 3 0 0 A straightforward computation gives Z 1 Z 1 q−r q−r (q − 1)(7q − 2r − 5) q−1 (1 − t) (2 + t) d t = t q−1 (3 − t) d t = , (2q − r − 1)(3q − r − 2) 0 0 Z 1 2p+1 (p + 4) − 2p − 5 (1 + t)p (2 − t) d t = . (p + 1)(p + 2) 0 (3.6) Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 146 b By the (α, m)-convexity of |f 00 |q on 0, m , we have 1 Z 00 2a + b q (1 − t) (2 + t) f ta + (1 − t) dt 3 Z 1 q 2a + b q (1 − t)r (2 + t) tα f 00 (a) +m(1 − tα ) f 00 ≤ dt 3m 0 q 3α + 2r + 5 B(α + 1, r + 1) f 00 (a) = α+r+2 00 2a + b q 2r + 5 3α + 2r + 5 ; +m − B(α + 1, r + 1) f (r + 1)(r + 2) α+r+2 3m r 0 1 Z 0 Z 0 00 2a + b a + 2b q (2 − t) f t +(1 − t) dt 3 3 q q Z 1 α 00 2a + b α 00 a + 2b ≤ + m(1 − t ) dt f (2 − t) t f 3 3m 0 q 00 2a + b 00 a + 2b q α+3 α(3α + 7) ; f = + m 2(α + 1)(α + 2) f (α + 1)(α + 2) 3 3m 1 q 00 a + 2b t (3 − t) f t +(1 − t)b) d t 3 q q Z 1 b α 00 r α 00 a + 2b + m(1 − t ) f dt ≤ t (3 − t) t f 3 m 0 00 a + 2b q 2α + 2r + 5 f = (α + r + 1)(α + r + 2) 3 q 00 b 2r + 5 2α + 2r + 5 f . +m − (r + 1)(r + 2) (α + r + 1)(α + r + 2) m r Substituting the equalities in (3.6) to the above inequalities and the inequality (3.5) yields the inequality (3.4). The proof of Theorem 3.6 is complete. Corollary 3.7. Under the conditions of Theorem 3.6, if α = m = 1, then ( 1/p Z b f (a) + f (b) (b − a)2 1 (q − 1)(7q − 2r − 5) − f (x) d x ≤ 2 b−a a 54 (2q − r − 1)(3q − r − 2) 00 q 00 2a + b q 1/q 2(r + 4) 2r + 7 f × f (a) + (r + 1)(r + 2)(r + 3) (r + 2)(r + 3) 3 p+1 1/p 1/q 2 (p + 4) − 2p − 5 2 00 2a + b q 5 00 a + 2b q + + f f (p + 1)(p + 2) 3 3 6 3 1/p 00 a + 2b q (q − 1)(7q − 2r − 5) 2r + 7 + f (2q − r − 1)(3q − r − 2) (r + 2)(r + 3) 3 1/q ) 00 q 2(r + 4) f (b) + . (r + 1)(r + 2)(r + 3) Theorem 3.8. Let f : R0 → R be twice differentiable and f 00 ∈ L([a, b]) for 0 ≤ a < b. If |f 00 |q is an b (α, m)-convex function on 0, m for (α, m) ∈ (0, 1]2 and q > 1, then Y. Shuang, F. Qi, Y. Wang, J. Nonlinear Sci. Appl. 9 (2016), 139–148 147 Z b f (a) + f (b) 1 f (x) d x − 2 b−a a 1/p 1/p (b − a)2 1 ≤ 3p+1 − 2p+1 (p + 2) 54 (p + 1)(p + 2) 00 q 00 2a + b q 1/q 1 − B (α + 1, q + 1) f × B (α + 1, q + 1) f (a) + m q+1 3m 00 2a + b q 1/p 2α + 3 p+1 + 2 (p + 4) − 2p − 5 f (α + 1)(α + 2) 3 00 a + 2b q 1/q 1/p 3α2 + 5α p+1 p+1 +m f + 3 − 2 (p + 2) 2(α + 1)(α + 2) 3m q 1/q ) q 00 a + 2b 00 b α 1 f +m f , × α+q+1 3 (α + q + 1)(q + 1) m where 1 p + 1 q = 1 and B(α, β) is the Beta function. b , by Lemma 2.1 and the Hölder integral inequality, we have Proof. Since |f 00 |q is (α, m)-convex on 0, m Z b f (a) + f (b) 1 − f (x) d x 2 b−a a (Z 1/p Z 1 1/q 1 2a + b q (b − a)2 p q 00 (2 + t) d t × (1 − t) f ta + (1 − t) ≤ d t 54 3 0 0 Z 1 1/p Z 1 1/q 00 2a + b a + 2b q p + (1 + t)(2 − t) d t (1 + t) f t + (1 − t) dt 3 3 0 0 Z 1 1/p Z 1 q 1/q ) a + 2b p q 00 + (3 − t) d t t f t + (1 − t)b d t 3 0 0 1/p 1/p 1 (b − a)2 3p+1 − 2p+1 (p + 2) ≤ 54 (p + 1)(p + 2) 00 q 00 2a + b q 1/q 1 × B (α + 1, q + 1) f (a) + m − B (α + 1, q + 1) f q+1 3m 00 2a + b q 00 a + 2b q 1/q 1/p 2α + 3 3α2 + 5α p+1 + 2 (p + 4) − 2p − 5 f + m 2(α + 1)(α + 2) f (α + 1)(α + 2) 3 3m q 1/q ) 00 a + 2b q 00 b 1/p α 1 p+1 p+1 f +m f + 3 −2 (p + 2) . α+q+1 3 (α + q + 1)(q + 1) m The proof of Theorem 3.8 is complete. Corollary 3.9. Under the conditions of Theorem 3.8, if α = m = 1, then Z b f (a) + f (b) 1 − f (x) d x 2 b−a a 1/p ( 1/p (b − a)2 1 ≤ × 3p+1 − 2p+1 (p + 2) 54 (p + 1)(p + 2) 1 1 00 2a + b q 1/q 00 q × |f (a)| + f (q + 1)(q + 2) q + 2 3 Y. Shuang, F. Qi, Y. Wang, J. 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