INVERSES OF NEW HILBERT-PACHPATTE-TYPE INEQUALITIES CHANG-JIAN ZHAO AND WING-SUM CHEUNG Received 7 February 2006; Revised 3 June 2006; Accepted 5 June 2006 We establish a new inequality of Hilbert type for a finite double number of nonnegative sequences of real numbers and some interrelated results, which are inverse and general forms of Pachpatte’s and Handley’s results. An integral version and some interrelated results are also obtained. These results provide some new estimates on such types of inequalities. Copyright © 2006 C.-J. Zhao and W.-S. Cheung. 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. 1. Introduction The various generalizations and sharpenings of Hilbert’s double series inequality and its integral version are obtained by Pachpatte, Handley et al., Gao et al. (see [1, 3, 5, 7, 10, 12, 16–18]). An elegant survey on this kind of inequalities was provided by Yang and Rassias (see [13]). Moreover, Pachpatte [9] established a new Hilbert-type inequality and its integral version as follows. Theorem 1.1. Let {am }, {bn } be two nonnegative sequences of real numbers defined for m = 1,2,...,k and n = 1,2,...,r with a0 = b0 = 0, and let { pm }, {qn } be two positive sequences 1,2,...,k, n = 1,2,...,r, where k, r are natural numbers. of real numbers defined for m = m n Define Pm = s=1 ps and Qn = t=1 qt . Let φ and ψ be two real-valued nonnegative, convex, and submultiplicative functions defined on R+ = [0, ∞). Then r k φ am ψ bn m=1 n=1 m+n ≤ M(k,r) k (k − m + 1) pm φ m=1 × r (r − n + 1) qn ψ n =1 Hindawi Publishing Corporation Journal of Inequalities and Applications Volume 2006, Article ID 97860, Pages 1–11 DOI 10.1155/JIA/2006/97860 ∇bn qn ∇ am 2 1/2 pm (1.1) 2 1/2 , 2 Inverses of new Hilbert-Pachpatte-type inequalities where 1 M(k,r) = 2 k m=1 φ Pm Pm 2 1/2 r n=1 φ Qn Qn 2 1/2 , (1.2) and ∇am = am − am−1 , ∇bn = bn − bn−1 . Theorem 1.2. Let f ∈ C 1 [[0,x), R+ ], g ∈ C 1 [[0, y), R+ ] with f (0) = g(0) = 0 and let p(σ), q(τ) be two positive functions defined for σ ∈ [0,x) and τ ∈ [0, y). Let P(s) = s t 0 p(σ)dσ and Q(t) = 0 q(τ)dτ for s ∈ [0,x) and t ∈ [0, y), where x, y are positive real numbers. Let φ, and ψ be as in Theorem 1.1. Then x y 0 0 φ f (s) ψ g(t) dsdt ≤ L(x, y) s+t × x 0 (x − s) p(s)φ g (t) (y − t) q(y)φ q(t) 0 y 2 f (s) p(s) 1/2 ds 2 (1.3) 1/2 dt , where 1 L(x, y) = 2 x φ P(s) P(s) 0 2 1/2 y ds φ Q(t) Q(t) 0 2 1/2 dt , (1.4) and denotes the derivative of a function. In [4], Handley et al. gave general versions of inequalities (1.1) and (1.3) as follows. Theorem 1.3. Let {ai,mi } (i = 1,2,...,n) be n sequences of nonnegative real numbers defined for mi = 1,2,...,ki with a1,0 = a2,0 = · · · = an,0 = 0, and let { pi,mi } be n sequences of positive real numbers defined for mi = 1,2,...,ki , where ki (i = 1,2,...,n) are natural numbers. i p Set Pi,mi = m si =1 i,si . Let φi (i = 1,2,...,n) be n real-valued nonnegative convex and submultiplicative functions defined on R+ . Let αi ∈ (0,1), and set αi = 1 − αi (i = 1,2,...,n), n n α = i=1 αi , and α = i=1 αi = n − α. Then k1 kn n i=1 φi ai,mi ··· n α m1 =1 mn =1 i=1 αi mi ≤ M k1 ,...,kn n i =1 ki ki − mi + 1 pi,mi φi mi =1 ∇ai,mi (1.5) 1/αi αi , pi,mi where M k1 ,...,kn n 1 = α (α ) i=1 and ∇ai,mi = ai,mi − ai,mi −1 (i = 1,2,...,n). ki mi =1 φi Pi,mi Pi,mi 1/αi αi , (1.6) C.-J. Zhao and W.-S. Cheung 3 Theorem 1.4. Let fi ∈ C 1 [[0,ki ], R+ ], i = 1,2,...,n, with fi (0) = 0 (i =1,2,...,n), let s pi (σi ) be n positive functions defined for σi ∈ [0,xi ] (i = 1,...,n). Set Pi (si ) = 0 i pi (σi )dσi for si ∈ [0,xi ], where xi are positive real numbers. Let φi , αi , αi , α, and α be as in Theorem 1.3. Then x1 0 ··· x n n 0 i=1 φi fi si n α i=1 αi si ≤ L x1 ,...,xn n ds1 · · · dsn 0 i=1 1/αi αi f si xi − si pi si φi i dsi , xi (1.7) pi si where L x1 ,...,xn αi n xi 1/αi φi Pi si 1 dsi . = α (α ) i=1 0 Pi si (1.8) The main purpose of the present paper is to establish their reverse versions, which are more extensive results for this type of inequalities. Our main results are given in the following theorems. Theorem 1.5. Let {asi ,ti ,msi ,mti } (i = 1,2,...,n) be n sequences of nonnegative numbers defined for msi = 1,2,...,ksi , mti = 1,2,...,kti , with asi ,ti ,0,mti = asi ,ti ,msi ,0 = 0 (i = 1,2,...,n), where ksi and kti (i = 1,2,...,n) are natural numbers. Let { psi ,ti ,msi ,mti } be n sequences of positive real numbers defined for msi , mti . Set Psi ,ti ,msi ,mti = msi mti mξi =1 mηi =1 psi ,ti ,mξi ,mηi (i = 1,2,...,n). (1.9) funcLet φi (i = 1,2,...,n) be n real-valued nonnegative concave and supermultiplicative n tions defined on R+ . Let αi ∈ (1, ∞). Set αi = 1 − αi (i = 1,2,...,n), α = i=1 αi , and α = n i=1 αi = n − α. Define operators ∇1 asi ,ti ,msi ,mti = asi ,ti ,msi ,mti − asi ,ti ,msi −1,mti , ∇2 asi ,ti ,msi ,mti = asi ,ti ,msi ,mti − asi ,ti ,msi ,mti −1 , ∇2 ∇1 asi ,ti ,msi ,mti = ∇2 ∇1 asi ,ti ,msi ,mti . (1.10) Then ks1 kt1 ··· ms1 =1 mt =1 ksn ktn msn =1 mtn =1 n i=1 φi (1/α ) n asi ,ti ,msi ,mti i=1 αi msi mti α ≥ C ks1 kt1 ,...,ksn ktn × ksi n i=1 kti msi =1 mti =1 ksi − msi +1 kti − mti +1 psi ,ti ,msi ,mti φi ∇2 ∇1 asi ,ti ,msi ,mti psi ,ti ,msi ,mti 1/αi αi , (1.11) 4 Inverses of new Hilbert-Pachpatte-type inequalities where C ks1 kt1 ,...,ksn ktn = n ksi kti msi =1 mti =1 i =1 φi Psi ,ti ,msi ,mti Psi ,ti ,msi ,mti 1/αi αi . (1.12) Theorem 1.6. Let fi (si ,ti ) (i = 1,2,...,n) be real-valued continuous functions defined on [0,xi ) × [0, yi ), where xi ∈ (0, ∞), yi ∈ (0, ∞), and with fi (0,ti ) = fi (si ,0) = 0 (i = 1,2,... ,n). Let pi (σi ) and qi (τi ) be positive continuous functions defined for σi ∈ (0,si ), τi ∈ (0,ti ). Set Pi si ,ti = ti s i 0 0 pi σi qi τi dσi dτi . (1.13) For the function fi (si ,ti ), denote the partial derivatives (∂/∂si ) fi (si ,ti ), (∂/∂ti ) fi (si ,ti ), and (∂2 /∂si ∂ti ) fi (si ,ti ) by D1 fi (si ,ti ), D2 fi (si ,ti ), and D2 D1 fi (si ,ti ) = D1 D2 fi (si ,ti ), respectively. Let φi , αi , αi , α, and α be as in Theorem 1.5. Then x1 y 1 0 0 ··· xn y n n 0 0 φi fi si ,ti (1/α ) i =1 n i=1 αi si ti α ds1 dt1 · · · dsn dtn = G x1 y1 ,...,xn yn × n xi y i 0 i=1 0 xi − si yi − ti pi si qi ti · φi αi 1/αi D2 D1 fi si ,ti pi si qi ti dsi dti , (1.14) where G x1 y1 ,...,xn yn αi 1/αi n xi y i φi Pi si ,ti dsi dti . = i=1 0 Pi si ,ti 0 (1.15) These results provide new estimates on these types of inequalities. 2. Proofs and remarks Proof of Theorem 1.5. From the operators defined in Theorem 1.5, we obtain asi ,ti ,msi ,mti = = msi mξi =1 msi asi ,ti ,mξi ,mti − asi ,ti ,mξi −1,mti mti mξi =1 mηi =1 = msi mti mξi =1 mηi =1 asi ,ti ,mξi ,mηi − asi ,ti ,mξi −1,mηi − asi ,ti ,mξi ,mηi −1 + asi ,ti ,mξi −1,mηi −1 ∇2 ∇1 asi ,ti ,mξi ,mηi . (2.1) C.-J. Zhao and W.-S. Cheung 5 From (2.1) and the hypotheses of Theorem 1.5, and in view of Jensen’s inequality and inverse Hölder’s inequality [6], we obtain φi asi ,ti ,msi ,mti = φi Psi ,ti ,msi ,mti msi mξi =1 mηi =1 msi mti mξi =1 mηi =1 psi ,ti ,mξi ,mηi φi φi Psi ,ti ,msi ,mti α ms i mt i i × ≥ Psi ,ti ,msi ,mti psi ,ti ,mξi ,mηi psi ,ti ,mξi ,mηi ∇2 ∇1 asi ,ti ,mξi ,mηi psi ,ti ,mξi ,mηi mξi =1 msi mti mξi =1 ≥ φi Psi ,ti ,msi ,mti · φi mηi =1 psi ,ti ,mξi ,mηi ∇2 ∇1 asi ,ti ,mξi ,mηi msi mti mξi =1 mηi =1 psi ,ti ,mξi ,mηi msi φi Psi ,ti ,msi ,mti ≥ Psi ,ti ,msi ,mti mti msi mti mηi =1 psi ,ti ,mξi ,mηi ∇2 ∇1 asi ,ti ,mξi ,mηi psi ,ti ,mξi ,mηi mti psi ,ti ,mξi ,mηi φi mξi =1 mηi =1 ∇2 ∇1 asi ,ti ,mξi ,mηi 1/αi αi . psi ,ti ,mξi ,mηi (2.2) On the other hand, noticing αi < 0 (i = 1,2,...,n), λi > 0 (i = 1,2,...,n), and applying the well-known means inequality, we have n 1 ≥ α λi α i=1 i α λi i i =1 n α . (2.3) Hence n i=1 φi (1/α ) ≥ n asi ,ti ,msi ,mti i=1 αi msi mti α msi n φi Psi ,ti ,msi ,mti i=1 Psi ,ti ,msi ,mti mti mξi =1 mηi =1 psi ,ti ,mξi ,mηi φi ∇2 ∇1 asi ,ti ,mξi ,mηi (2.4) 1/αi αi psi ,ti ,mξi ,mηi . Taking the sum of both sides of (2.4) over msi , mti (i = 1,2,...,n) from 1 to ksi , ksi , respectively, and in view of inverse Hölder’s inequality, we get ks1 kt1 ··· ms1 =1 mt =1 ksi n ≥ ktn ksn msn =1 mtn =1 kti i=1 msi =1 mti =1 n i=1 φi (1/α ) n φi Psi ,ti ,msi ,mti Psi ,ti ,msi ,mti asi ,ti ,msi ,mti i=1 αi msi mti msi α mti mξi =1 mηi =1 psi ,ti ,mξi ,mηi φi ∇2 ∇1 asi ,ti ,mξi ,mηi psi ,ti ,mξi ,mηi 1/αi αi 6 Inverses of new Hilbert-Pachpatte-type inequalities ≥ n ksi kti φi Psi ,ti ,msi ,mti Psi ,ti ,msi ,mti msi =1 mti =1 i=1 ksi × kti msi =1 mti =1 mti msi mξi =1 mηi =1 1/αi αi psi ,ti ,mξi ,mηi φi ∇2 ∇1 asi ,ti ,mξi ,mηi 1/αi αi psi ,ti ,mξi ,mηi = C ks1 kt1 ,...,ksn ktn × ksi n kti ksi − mξi +1 kti − mηi +1 i=1 mξi =1 mηi =1 psi ,ti ,mξi ,mηi φi ∇2 ∇1 asi ,ti ,mξi ,mηi 1/αi αi psi ,ti ,mξi ,mηi = C ks1 kt1 ,...,ksn ktn × ksi n kti i=1 msi =1 mti =1 ksi − msi +1 kti − mti +1 psi ,ti ,msi ,mti φi ∇2 ∇1 asi ,ti ,msi ,mti 1/αi αi . psi ,ti ,msi ,mti (2.5) This completes the proof. Remark 2.1. Let asi ,ti ,msi ,mti , msi , mti , ksi , kti , asi ,ti ,0,mti , asi ,ti ,msi ,0 , Psi ,ti ,msi ,mti , ∇1 , and ∇2 be as in Theorem 1.5. Let φi , αi , αi , α, and α (i = 1,2,...,n) be as in Theorem 1.3. Similar to the proof of Theorem 1.5, we obtain ks1 kt1 ··· ms1 =1 mt =1 ksn ktn n i=1 φi asi ,ti ,msi ,mti n α msn =1 mtn =1 i=1 αi msi mti ≤ C ks1 kt1 ,...,ksn ktn × n ksi kti msi =1 mti =1 i=1 ksi − msi +1 kti − mti +1 psi ,ti ,msi ,mti φi ∇2 ∇1 asi ,ti ,msi ,mti 1/αi αi , psi ,ti ,msi ,mti (2.6) where C ks1 kt1 ,...,ksn ktn n 1 = α (α ) i=1 ksi kti msi =1 mti =1 φi Psi ,ti ,msi ,mti Psi ,ti ,msi ,mti 1/αi αi . (2.7) This is just a general form of inequality (1.5) and the inverse form of inequality (1.11). C.-J. Zhao and W.-S. Cheung 7 Moreover, let {ai,mi }, mi , ki , ai,0 , pi,mi , ∇, and Pi,mi (i = 1,2,...,n) be as in Theorem 1.3. Let φi , αi , αi , α, and α (i = 1,2,...,n) be as in Theorem 1.5. Similar to the proof of Theorem 1.5, we obtain k1 n kn i=1 φi ai,mi ··· n α m1 =1 mn =1 (1/α ) i=1 αi mi ≥ M k1 ,...,kn n ki ki − mi + 1 pi,mi φi ∇ai,mi , pi,mi mi =1 i =1 (2.8) 1/αi αi where n M k1 ,... ,kn = ki mi =1 i =1 φi Pi,mi Pi,mi 1/αi αi . (2.9) This is just an inverse form of inequality (1.5) which was given by Handley et al. [4]. Let n = 2, α1 = α2 = 2, then α1 = α2 = −1, putting them in inequality (2.8), we have k2 k1 φ1 a1,m1 φ2 a2,m2 −2 m 1 + m2 m1 =1 m2 =1 ≥ M k1 ,k2 × k1 k1 − m1 + 1 m1 =1 k2 k2 − m2 + 1 p1,mi φ1 p2,m2 φ2 1/2 2 (2.10) p1,m1 ∇a2,m2 m2 =1 ∇a1,m1 1/2 2 p2,m2 , where M k1 ,k2 = 4 k1 m1 =1 φ1 P1,m1 P1,m1 −1 −1 k2 m2 =1 φ2 P2,m2 P2,m2 −1 −1 . (2.11) This is just an inverse form of inequality (1.1) which was given by Pachpatte [9]. Proof of Theorem 1.6. From the hypotheses of Theorem 1.6, we obtain fi si ,ti = s i ti 0 0 D2 D1 fi σi ,τi dσi dτi . (2.12) 8 Inverses of new Hilbert-Pachpatte-type inequalities From (2.12) and using Jensen’s integral inequality and Hölder’s integral inequality [6], we obtain φi fi si ,ti = φi Pi si ,ti ≥ φi Pi si ,ti ti s i ti s i 0 0 · φi t s i i φi (Pi si ,ti Pi si ,ti ≥ 0 pi σi qi τi D2 D1 fi σi ,τi pi σi qi τi dσi dτi ti s i 0 0 pi σi qi τi dσi dτi 0 0 0 φi Pi si ,ti αi ≥ si ti Pi si ,ti pi σi qi τi D2 D1 fi σi ,τi / pi σi qi τi dσi dτi ti s i 0 0 pi σi qi τi dσi dτi pi σi qi τi · φi ti s i 0 0 D2 D1 fi σi ,τi pi σi qi τi pi σi qi τi · φi dσi dτi D2 D1 fi σi ,τi pi σi qi τi αi 1/αi dσi dτi . (2.13) From the well-known inequality for means, we have n φi fi si ,ti (1/α ) i=1 n i=1 αi si ti α αi t s 1/αi n i i φi Pi si ,ti D2 D1 fi σi ,τi ≥ pi σi qi τi · φi dσi dτi . Pi si ,ti i=1 0 pi σi qi τi 0 (2.14) Integrating both sides of (2.14) over si , ti from 1 to xi , yi (i = 1,2,...,n) and in view of Hölder’s integral inequality and Fubini’s theorem, we observe that x1 y 1 0 0 ≥ ··· xn y n n 0 0 φi fi si ,ti (1/α ) i=1 n i=1 αi si ti α ds1 dt1 · · · dsn dtn n xi y i φi Pi si ,ti i=1 0 Pi si ,ti 0 ti s i × 0 0 pi σi qi τi · φi 1/αi D2 D1 fi σi ,τi pi σi qi τi αi dσi dτi dsi dti αi 1/αi n xi y i φi Pi si ,ti ≥ dsi dti i=1 × 0 Pi si ,ti 0 xi y i ti s i 0 0 0 0 pi σi qi τi · φi 1/αi D2 D1 fi σi ,τi pi σi qi τi dσi dτi dsi dti αi C.-J. Zhao and W.-S. Cheung 9 = G x1 y1 ,...,xn yn × n xi y i 0 i=1 xi − si yi − ti 0 pi si qi ti · φi αi 1/αi D2 D1 fi si ,ti pi si qi ti dsi dti . (2.15) The proof is complete. Remark 2.2. Let fi (si ,ti ), xi , yi , fi (0,ti ), fi (si ,0), D1 fi (si ,ti ), D2 fi (si ,ti ), D2 D1 fi (si ,ti ), pi (σi ), qi (τi ), and Pi (si ,ti ) be as in Theorem 1.6. Let φi , αi , αi , α, and α be as in Theorem 1.3. Similar to the proof of Theorem 1.6, we have x1 y 1 0 0 ··· xn y n n 0 0 φi fi si ,ti α ds1 dt1 · · · dsn dtn n i=1 αi si ti i =1 ≤ G x1 y1 ,...,xn yn × n xi y i 0 i=1 xi − si yi − ti 0 pi si qi ti · φi 1/αi D2 D1 fi si ,ti pi si qi ti αi dsi dti , (2.16) where G x1 y1 ,...,xn yn αi 1/αi n xi y i φi Pi si ,ti 1 dsi dti . = α (α ) i=1 0 0 Pi si ,ti (2.17) This is just a general form of inequality (1.7) and an inverse form of the inequality (1.14). On the other hand, let fi , fi (0), fi (si ), pi (σi ), σi , ki , si , xi , Pi (si ) be as in Theorem 1.4, and let φi , αi , αi , α, α be as in Theorem 1.5. Then x1 0 ··· xn 0 n i=1 φi (1/α ) n ≥ L x1 ,...,xn fi si i=1 αi si n 1/αi αi f si xi − si pi si φi i dsi , xi 0 i =1 α ds1 · · · dsn (2.18) pi si where L x1 ,...,xn αi n xi 1/αi φi Pi si dsi . = i=1 0 Pi si (2.19) This is just an inverse form of inequality (1.7) which was given by Handley et al. [4]. 10 Inverses of new Hilbert-Pachpatte-type inequalities Let n = 2, α1 = α2 = 2, then α1 = α2 = −1, taking them in inequality (2.18), we have x1 x2 0 φ1 f1 s1 φ2 f2 s2 s1 + s2 0 ≥ L x1 ,x2 × ds1 ds2 x1 0 x2 0 −2 x2 − s2 x1 − s1 p1 s1 φ1 p2 s2 φ2 1/2 f2 s1 p1 s1 ds1 (2.20) 2 1/2 f2 s2 p2 s2 2 ds2 , where L x1 ,x2 = 4 x1 0 −1 −1 φ1 P1 s1 P1 s1 ds1 x2 0 −1 −1 φ2 P2 s2 P2 s2 ds2 . (2.21) This is just an inverse form of inequality (1.3) which was given by Pachpatte [9]. For interrelated research on similar inequalities, one is referred to [2, 8, 11, 14, 15], and the references cited therein. Acknowledgments Research of the first author is supported by Zhejiang Provincial Natural Science Foundation of China (Y605065), National Natural Sciences Foundation of China (10271071), Foundation of the Education Department of Zhejiang Province of China (20050392), and the Academic Mainstay of Middle-age and Youth Foundation of Shandong Province of China (200203). 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Debnath, Some new inverse type Hilbert integral inequalities, Journal of Mathematical Analysis and Applications 262 (2001), no. 1, 411–418. Chang-Jian Zhao: Department of Information and Mathematics Sciences, College of Science, China Jiliang University, Hangzhou 310018, China E-mail address: chjzhao@cjlu.edu.cn Wing-Sum Cheung: Department of Mathematics, The University of Hong Kong, Pokfulam Road, Hong Kong E-mail address: wscheung@hku.hk