Journal of Inequalities in Pure and Applied Mathematics http://jipam.vu.edu.au/ Volume 7, Issue 4, Article 154, 2006 ON SEVERAL NEW INEQUALITIES CLOSE TO HILBERT-PACHPATTE’S INEQUALITY BING HE AND YONGJIN LI D EPARTMENT OF M ATHEMATICS S UN YAT- SEN U NIVERSITY G UANGZHOU , 510275 P. R. C HINA hzs314@163.com stslyj@mail.sysu.edu.cn Received 27 April, 2006; accepted 09 October, 2006 Communicated by B. Yang A BSTRACT. In this paper we establish several new inequalities similar to Hilbert-Pachpatte’s inequality. Moreover, some new generalizations of Hilbert-Pachpatte’s inequality are presented. Key words and phrases: Hilbert’s inequality, Hölder’s inequality, Jensen’s inequality, Power mean inequality. 2000 Mathematics Subject Classification. 26D15. 1. I NTRODUCTION The well known Hardy-Hilbert’s inequality is (see [1]): P P∞ p0 p Theorem 1.1. If p > 1, p0 = p/(p − 1) and ∞ m=1 am ≤ A, n=1 bn ≤ B, then ∞ X ∞ X 1 1 am bn π (A) p (B) p0 , (1.1) < m+n sin πp n=1 m=1 unless the sequence {am } or {bn } is null. The integral analogue can be stated as follows: R∞ R∞ 0 Theorem 1.2. If p > 1, p0 = p/(p − 1) and 0 f p (x)dx ≤ F, 0 g p (y)dy ≤ G, then Z ∞Z ∞ 1 1 f (x)g(y) π F p G p0 (1.2) dxdy < x+y 0 0 sin πp unless f ≡ 0 or g ≡ 0. The following two theorems were studied by Pachpatte (see [2]) ISSN (electronic): 1443-5756 c 2006 Victoria University. All rights reserved. The work was partially supported by the Foundation of Sun Yat-sen University Advanced Research Centre. 124-06 2 B ING H E AND YONGJIN L I Theorem 1.3. Let p ≥ 1, q ≥ 1 and f (σ) ≥ 0, Rg(τ ) ≥ 0 for σ ∈ R(0, x), τ ∈ (0, y), where s t x, y are positive real numbers and define F (s) = 0 f (σ)dσ, G(t) = 0 g(τ )dτ , for s ∈ (0, x), t ∈ (0, y). Then Z x 21 Z xZ y p F (s)Gq (t) p−1 2 dsdt ≤ D(p, q, x, y) (x − s)(F (s)f (s)) ds s+t 0 0 0 Z y 12 q−1 2 × (y − t)(G (t)g(t)) dt , 0 unless f ≡ 0 or g ≡ 0, where 1 √ D(p, q, x, y) = pq xy. 2 Theorem 1.4. Let f, g, F, G be as in the above theorem, let p(σ) R s and q(τ ) be twoR tpositive functions defined for σ ∈ (0, x), τ ∈ (0, y) and define P (s) = 0 p(σ)dσ, Q(t) = 0 q(τ )dτ for s ∈ (0, x), t ∈ (0, y), where x, y are positive real numbers. Let φ and ψ be real-valued, nonnegative, convex, and sub-multiplicative functions defined on R+ = [0, ∞). Then (Z 2 ) 12 Z xZ y x f (s) φ(F (s))ψ(G(t)) (1.3) dsdt ≤ L(x, y) (x − s) p(s)φ ds s+t p(s) 0 0 0 (Z 2 ) 12 y g(t) × (y − t) q(t)ψ dt q(t) 0 where x Z 1 L(x, y) = 2 0 φ(P (s)) P (s) ! 12 2 Z y ds 0 ψ(Q(t)) Q(t) 2 ! 12 dt . The inequalities in these theorems were studied extensively and numerous variants, generalizations, and extensions have appeared in the literature (see [3] – [9]). The main purpose of the present article is to establish some new inequalities similar to the Hilbert-Pachpatte inequalities. 2. M AIN R ESULTS Lemma 2.1. Suppose p > 1, p1 + 1q = 1, r > 1, 1r + w1 = 1, λ > 0, define the weight functions ω e1 (w, p, x), ω e2 (w, p, x), ω e3 (w, p, x) as Z ∞ λ 1 x(p−1)(1− r ) dy, x ∈ (0, ∞), (2.1) ω e1 (w, p, x) := · λ xλ + y λ y 1− w 0 ∞ Z (2.2) ω e2 (w, p, x) := 0 Z (2.3) ω e3 (w, p, x) := λ 1 x(p−1)(1− r ) dy, · λ max {xλ , y λ } y 1− w ∞ 0 ω e1 (w, p, x) = J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 λ ln x/y x(p−1)(1− r ) dy, · λ xλ − y λ y 1− w Then x ∈ (0, ∞), π λ sin x ∈ (0, ∞). λ π r xp(1− r )−1 , http://jipam.vu.edu.au/ O N I NEQUALITIES C LOSE TO H ILBERT-PACHPATTE ’ S I NEQUALITY 3 rw p(1− λ )−1 r x , λ #2 " λ π xp(1− r )−1 . ω e3 (w, p, x) = π λ sin r ω e2 (w, p, x) = Proof. For fixed x, let u = y λ /xλ , then (2.1) turns into Z 1 1 p(1− λ )−1 ∞ 1 r u−1+ w du ω e1 (w, p, x) = x λ 1+u 0 1 1 1 p(1− λ )−1 r = x B , λ w r λ π xp(1− r )−1 = λ sin πp and similarly, we can prove the others. Theorem 2.2. Let m ≥ 1, n ≥ 1, pi > 1, p1i + q1i = 1 for i = 0, 1, 2, 3, 4, p0 = p, p3 = k, Rs p4 = r; q0 = q, q3 = l, q4 = w and f (σ) ≥ 0, g(τ ) ≥ 0. Define F (s) = 0 f (σ)dσ and Rt G(t) = 0 g(τ )dτ such that Z ∞ Z ∞ λ p(1− λ )−1 p r 0< s Ff (s)ds < ∞, 0< tq(1− w )−1 Gqg (t)dt < ∞ 0 0 for σ, τ, s, t ∈ (0, ∞). Then Z ∞Z ∞ F m (s)Gn (t) (2.4) dsdt (lsk/p1 + ktl/p2 )(sλ + tλ ) 0 0 p1 Z Z ∞ p p(1− λ )−1 r Ff (s)ds ≤ E1 (m, n, k, r, λ) s unless f ≡ 0 or g ≡ 0, where E1 (m, n, k, r, λ) = Ff (s) = (F t 1q Gqg (t)dt πmn , λkl sin(π/r) q1 s m−1 λ q(1− w )−1 0 0 Z ∞ q1 1 (σ)f (σ)) dσ and 0 t Z (Gn−1 (τ )g(τ ))q2 dτ Gg (t) = q1 2 . 0 Proof. From the hypotheses, we can easily observe that Z s m (2.5) F (s) = m F m−1 (σ)f (σ)dσ, s ∈ (0, ∞), 0 (2.6) n Z G (t) = n t Gn−1 (τ )g(τ )dτ, t ∈ (0, ∞). 0 From (2.5) and (2.6), applying Hölder’s inequality, equality (2.1) and Young’s inequality: ab ≤ J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 ap bq + , p q http://jipam.vu.edu.au/ 4 B ING H E AND YONGJIN L I where a ≥ 0, b ≥ 0, p > 1, 1 p + 1 q = 1, we obtain F m (s)Gn (t) Z t Z s m−1 n−1 = mn F (σ)f (σ)dσ G (τ )g(τ )dτ 0 ≤ mns 0 1/p1 1/p2 Z s t (F m−1 q1 Z t q1 2 1 n−1 q2 (σ)f (σ)) dσ) (G (τ )g(τ )) dτ ) q1 0 ≤ mn sk/p1 k 0 Z s q1 Z t q1 2 1 tl/p2 + (F m−1 (σ)f (σ))q1 dσ) (Gn−1 (τ )g(τ ))q2 dτ ) . l 0 0 Note that Z Ff (s) = q1 s (F m−1 q1 (σ)f (σ)) dσ 1 Z , Gg (t) = (G n−1 q2 (τ )g(τ )) dτ q1 2 . 0 0 Hence Z ∞Z t ∞ F m (s)Gn (t) dsdt (lsk/p1 + ktl/p2 )(sλ + tλ ) 0 0 n o1 1 Z ∞ Z ∞ R s (F m−1 (σ)f (σ))q1 dσ) q1 R t (Gn−1 (τ )g(τ ))q2 dτ ) q2 0 0 mn ≤ dsdt λ λ kl 0 s +t 0 #" # " Z Z λ λ t(1− w )/p 1 s(1− r )/q mn ∞ ∞ Gg (t) dsdt Ff (s) = λ λ kl 0 sλ + tλ t(1− w )/p s(1− r )/q 0 (Z Z ) p1 (Z Z ) 1q λ ∞ ∞ F p (s) ∞ ∞ Gq (t) (p−1)(1− λ ) (q−1)(1− w ) r mn s t f g ≤ · dsdt · dsdt λ λ λ + tλ λ + tλ (1− w ) kl s s t s(1− r ) 0 0 0 0 Z ∞ p1 Z ∞ 1q mn p q = ω e1 (w, p, s)Ff (s)ds ω e1 (r, q, t)Gg (t)dt kl 0 0 p1 Z ∞ 1q Z ∞ λ πmn p )−1 q(1− )−1 q p(1− λ r w t = s Ff (s)ds Gg (t)dt λkl sin(π/r) 0 0 1q p1 Z ∞ Z ∞ λ )−1 q p(1− λ )−1 p q(1− w r t Gg (t)dt . = E1 (m, n, k, r, λ) s Ff (s)ds 0 0 This completes the proof. Theorem 2.3. Let m ≥ 1, n ≥ 1, pi > 1, p1i + q1i = 1 for i = 0, 1, 2, 3, 4, p0 = p, p3 = k, Rs p4 = r; q0 = q, q3 = l, q4 = w and f (σ) ≥ 0, g(τ ) ≥ 0. Define F (s) = 0 f (σ)dσ and R∞ Rt R∞ λ λ G(t) = 0 g(τ )dτ such that 0 < 0 sp(1− r )−1 Ffp (s)ds < ∞, 0 < 0 tq(1− w )−1 Gqg (t)dt < ∞ for σ, τ, s, t ∈ (0, ∞). Then Z ∞Z ∞ F m (s)Gn (t) dsdt (lsk/p1 + ktl/p2 ) max{sλ , tλ } 0 0 1q Z ∞ p1 Z ∞ λ )−1 q p(1− λ )−1 p q(1− w r Gg (t)dt , Ff (s)ds t ≤ E2 (m, n, k, r, λ) s 0 J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 0 http://jipam.vu.edu.au/ O N I NEQUALITIES C LOSE TO H ILBERT-PACHPATTE ’ S I NEQUALITY unless f ≡ 0 or g ≡ 0, where E2 (m, n, k, r, λ) = mnrw λkl and q1 s Z Ff (s) = (F m−1 (G n−1 5 q1 1 (σ)f (σ)) dσ , 0 t Z Gg (t) = q2 q1 2 (τ )g(τ )) dτ . 0 Proof. By (2.5) and (2.6), using Hölder’s inequality, equality (2.2) and Young’s inequality: p q ab ≤ ap + bq , where a ≥ 0, b ≥ 0, p > 1, p1 + 1q = 1. We obtain F m (s)Gn (t) Z s Z t m−1 n−1 = mn F (σ)f (σ)dσ G (τ )g(τ )dτ 0 ≤ mns 0 1/p1 1/p2 Z s t (F m−1 q1 Z t q1 2 1 n−1 q2 (σ)f (σ)) dσ) (G (τ )g(τ )) dτ ) q1 0 ≤ mn sk/p1 k 0 Z s q1 Z t q1 2 1 tl/p2 + (F m−1 (σ)f (σ))q1 dσ) (Gn−1 (τ )g(τ ))q2 dτ ) . l 0 0 Note Z q1 s Ff (s) = (F m−1 (G n−1 q1 1 (σ)f (σ)) dσ , 0 Z Gg (t) = t q2 (τ )g(τ )) dτ q1 2 . 0 Hence Z ∞Z ∞ F m (s)Gn (t) dsdt (lsk/p1 + ktl/p2 ) max{sλ , tλ } 0 0 n o1 1 Z ∞ Z ∞ R s (F m−1 (σ)f (σ))q1 dσ) q1 R t (Gn−1 (τ )g(τ ))q2 dτ ) q2 0 0 mn ≤ dsdt λ kl 0 max{s , tλ } 0 # #" " Z Z λ λ t(1− w )/p mn ∞ ∞ 1 s(1− r )/q dsdt Gg (t) = Ff (s) λ λ kl 0 max{sλ , tλ } s(1− r )/q t(1− w )/p 0 ) 1q ) p1 (Z Z (Z Z λ λ ∞ ∞ ∞ ∞ Ffp (s) s(p−1)(1− r ) Gqg (t) mn t(q−1)(1− w ) dsdt dsdt ≤ max{sλ , tλ } s(1− λr ) kl max{sλ , tλ } t(1− wλ ) 0 0 0 0 Z ∞ p1 Z ∞ 1q mn p q = ω e2 (w, p, s)Ff (s)ds ω e2 (r, q, t)Gg (t)dt kl 0 0 1q p1 Z ∞ Z ∞ λ mnrw p )−1 q )−1 q(1− p(1− λ w r Gg (t)dt Ff (s)ds t = s λkl 0 0 Z ∞ p1 Z ∞ 1q λ λ p tq(1− w )−1 Gqg (t)dt . = E2 (m, n, k, r, λ) sp(1− r )−1 Ff (s)ds 0 This completes the proof. J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 0 http://jipam.vu.edu.au/ 6 B ING H E AND YONGJIN L I Theorem 2.4. Let m ≥ 1, n ≥ 1, pi > 1, p1i + q1i = 1 for i = 0, 1, 2, 3, 4, p0 = p, p3 = k, Rs p4 = r; q0 = q, q3 = l, q4 = w and f (σ) ≥ 0, g(τ ) ≥ 0. Define F (s) = 0 f (σ)dσ and Rt G(t) = 0 g(τ )dτ such that Z ∞ λ 0< sp(1− r )−1 Ffp (s)ds < ∞, Z0 ∞ λ 0< tq(1− w )−1 Gqg (t)dt < ∞ 0 for σ, τ, s, t ∈ (0, ∞). Then Z ∞ 0 Z 0 ∞ ln(s/t) (sλ − tλ )(lsk/p1 F m (s)Gn (t)dsdt ≤ E3 (m, n, k, r, λ) + ktl/p2 ) Z ∞ p1 Z ∞ 1q λ p p(1− λ )−1 )−1 q q(1− r w × s Ff (s)ds Gg (t)dt , t 0 0 unless f ≡ 0 or g ≡ 0, where E3 (m, n, k, r, λ) = Z π 2 mn , λ2 kl(sin(π/r))2 q1 s Ff (s) = (F m−1 (G n−1 q1 1 (σ)f (σ)) dσ , 0 Z q1 t Gg (t) = 2 q2 (τ )g(τ )) dτ . 0 Proof. From (2.5) and (2.6), by Hölder’s inequality, equality (2.3) and Young’s inequality: ab ≤ q ap + bq , where a ≥ 0, b ≥ 0, p > 1, p1 + 1q = 1, and using a similar method of proof to that of p Theorem 2.2, the result can be clearly seen. P Theorem 2.5. Let mi ≥ 1, pi > 1, ni=1 p1i = 1, p1i + q1i = 1, and fi (σi ) ≥ 0 for σi ∈ Rt (0, xi ), where xi are positive real numbers and define Fi (ti ) = 0 i fi (σi )dσi , for ti ∈ (0, xi ), i = 1, 2, . . . , n. Then Z x1 Z x2 Z xn Q n mi i=1 Fi (ti ) Pn ti dt1 dt2 · · · dtn (2.7) ··· 0 0 0 i=1 pi ≤ n Y Z D(mi , xi , pi ) xi qi q1i e (xi − ti ) Fi (ti ) dti , 0 i=1 1 p unless f ≡ 0 or g ≡ 0, where D(mi , xi , pi ) = mi xi i , Fei (ti ) = F mi −1 (ti )fi (ti ). Proof. From the hypotheses, we know that Z ti (m −1) mi (2.8) Fi (ti ) = mi Fi i (σi )fi (σi )dσi , ti ∈ (0, xi ). 0 Then (2.9) n Y Fimi (ti ) i=1 J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 = n Y i=1 Z mi ti Fimi −1 (σi )fi (σi )dσi . 0 http://jipam.vu.edu.au/ O N I NEQUALITIES C LOSE TO H ILBERT-PACHPATTE ’ S I NEQUALITY 7 Using Hölder’s inequality, we have ti Z Fimi −1 (σi )dσi (2.10) 1 pi Z 1 pi Z ti ≤ ti 0 (Fimi −1 (σi )fi (σi ))qi dσi q1 i 0 ti , ti q1 qi i e Fi (σi ) dσi . 0 By (2.9) and (2.10) it follows that n Y Fimi (ti ) ≤ i=1 n Y ti Z 1 pi mi ti q1 qi i e Fi (σi ) dσi . 0 i=1 Applying Young’s inequality n Y n X 1 |ak |pk , p k k=1 |ak | ≤ k=1 where 1 < pk < ∞, Pn 1 k=1 pk = 1, we observe that Qn Z n mi Y i=1 Fi (ti ) Pn ti ≤ mi i=1 pi ti q1 qi i . Fei (σi ) dσi 0 i=1 Integrating over ti from 0 to xi where i runs from 1 to n, and using the Hölder’s inequality, we get Z x1 Z x2 Z xn Q n mi i=1 Fi (ti ) Pn ti dt1 dt2 · · · dtn ··· 0 0 0 i=1 pi ≤ n Y "Z ≤ i=1 = n Y i=1 ti Z mi 0 i=1 n Y xi 1 pi q1 qi i Fei (σi ) dσi dti # 0 Z xi ti Z mi xi 0 q1 qi i Fei (σi ) dσi dti 0 Z D(mi , xi , pi ) xi qi q1i e (xi − ti ) Fi (ti ) dti 0 This completes the proof. Remark 2.6. In the special case when p1 = p2 = · · · = pn = n, the inequality (2.7) reduces to the following inequality, Z x1 Z x2 Z ··· (2.11) 0 0 0 xn Qn F mi (ti ) i=1 Pn i dt1 dt2 · · · dtn i=1 ti n−1 Z xi n n n−1 n 1Y e ≤ dti D(mi , xi ) (xi − ti ) Fi (ti ) n i=1 0 J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 http://jipam.vu.edu.au/ 8 B ING H E AND YONGJIN L I 1 where D(mi , xi ) = mi xin . Moreover, (i) (2.11) reduces to Theorem 1.3 which belongs to Pachpatte for n = 2; (ii) when m1 = m2 = · · · = mn = 1, (2.11) turns into x1 Z Z x2 Z xn ··· (2.12) 0 0 0 Qn i=1 Fi (ti ) P dt1 dt2 · · · dtn n i=1 ti n−1 Z xi n n n 1Y ≤ D(mi , xi ) (xi − ti )(fi (ti )) n−1 dti n i=1 0 Theorem 2.7. Let fi , Fi be as in the above theorem, p > 1, p1i + q1i = 1, let pi (σi ) be positive Rt function defined for σi ∈ (0, xi ), and define Pi (ti ) = 0 i pi (σi )dσi for ti ∈ (0, xi ),where xi are positive real numbers. Let φi be real-valued, nonnegative, convex, and sub-multiplicative function defined on R+ = [0, ∞), i = 1, 2, . . . , n. Then x1 Z Z x2 Z xn Qn 0 0 0 ≤ φ (F (t )) Pni tii i dt1 dt2 · · · dtn i=1 ··· (2.13) i=1 pi n Y Z L(xi , pi ) 0 i=1 xi qi q1 i fi (ti ) (xi − ti ) pi (ti )φi dti , pi (ti ) where Z xi L(xi , pi ) = 0 φi (Pi (ti )) Pi (ti ) p1 pi dti i . Proof. Applying Jensen’s inequality and Hölder’s inequality, it is clear to observe that ! Rt i) Pi (ti ) 0 i pi (σi ) pfii (σ dσi (σi ) φi (Fi (ti )) = φi R ti pi (σi )dσi 0 Z ti φi (Pi (ti )) fi (σi ) ≤ pi (σi )φi dσi Pi (ti ) pi (σi ) 0 Z ti qi q1 i φi (Pi (ti )) p1i fi (σi ) ≤ ti pi (σi )φi dσi . Pi (ti ) pi (σi ) 0 Using Young’s inequality, we obtain that Qn n Y φi (Pi (ti )) i=1 φi (Fi (ti )) Pn ti ≤ Pi (ti ) i=1 pi i=1 J. Inequal. Pure and Appl. Math., 7(4) Art. 154, 2006 Z 0 ti qi q1 i fi (σi ) pi (σi )φi dσi . pi (σi ) http://jipam.vu.edu.au/ O N I NEQUALITIES C LOSE TO H ILBERT-PACHPATTE ’ S I NEQUALITY 9 Integrating both sides of the above inequality over ti from 0 to xi with i running from i to n, and applying the Hölder inequality, we get Z x1 Z x2 Z xn Q n i=1 φi (Fi (ti )) Pn ti ··· dt1 dt2 · · · dtn 0 0 0 i=1 pi # qi q1 ti i φi (Pi (ti )) fi (σi ) ≤ pi (σi )φi dσi dti P (t ) p (σ ) i i i i 0 0 i=1 qi q1 p p1 Z xi Z ti n Z xi Y i i fi (σi ) φi (Pi (ti )) i dσi dti ≤ dti pi (σi )φi pi (σi ) Pi (ti ) 0 0 0 i=1 1 p p Z xi qi q1 n Z xi Y i i φi (Pi (ti )) i fi (ti ) = (xi − ti ) pi (ti )φi dti dti Pi (ti ) pi (ti ) 0 0 i=1 Z xi qi q1 n Y i fi (ti ) dti = L(xi , pi ) (xi − ti ) pi (ti )φi pi (ti ) 0 i=1 n Y "Z xi Z This completes the theorem. R EFERENCES [1] G.H. HARDY, J.E. LITTLEWOOD bridge, 1952. AND G. POLYA, Inequalities, Cambridge Univ. Press, Cam- [2] B.G. 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