<p>A well-known theorem due to Ankeny and Rivlin states that if <i>p</i>(<i>z</i>) is a polynomial of degree <i>n</i> such that <i>p</i>(<i>z</i>) has no zero in <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="51" /> </InlineMediaObject> <EquationSource Format="TEX">\(|z|&lt;1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>z</mi> <mo stretchy="false">|</mo> <mo>&lt;</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, then <Equation ID="Equ45"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_Equ45.gif" Format="GIF" Height="43" Rendition="HTML" Resolution="72" Type="Linedraw" Width="269" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \max _{|z|=R\ge 1}|p(z)|\le \left( \frac{R^{n}+1}{2}\right) \max _{|z|=1}|p(z)|. \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <munder> <mo movablelimits="true">max</mo> <mrow> <mo stretchy="false">|</mo> <mi>z</mi> <mo stretchy="false">|</mo> <mo>=</mo> <mi>R</mi> <mo>≥</mo> <mn>1</mn> </mrow> </munder> <mrow> <mo stretchy="false">|</mo> <mi>p</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> <mo>≤</mo> <mfenced close=")" open="("> <mfrac> <mrow> <msup> <mi>R</mi> <mi>n</mi> </msup> <mo>+</mo> <mn>1</mn> </mrow> <mn>2</mn> </mfrac> </mfenced> <munder> <mo movablelimits="true">max</mo> <mrow> <mo stretchy="false">|</mo> <mi>z</mi> <mo stretchy="false">|</mo> <mo>=</mo> <mn>1</mn> </mrow> </munder> <mrow> <mo stretchy="false">|</mo> <mi>p</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> <mo>.</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>This research investigates the polynomial <i>p</i>(<i>z</i>) ensuring it possesses no zero in <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="55" /> </InlineMediaObject> <EquationSource Format="TEX">\(|z|&lt;k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>z</mi> <mo stretchy="false">|</mo> <mo>&lt;</mo> <mi>k</mi> </mrow> </math></EquationSource> </InlineEquation> where <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(k\ge 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. Simultaneously, we explore the <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq4.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(s^{th}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>s</mi> <mrow> <mi mathvariant="italic">th</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> derivative, where <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq5.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="75" /> </InlineMediaObject> <EquationSource Format="TEX">\(0\le s&lt;n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0</mn> <mo>≤</mo> <mi>s</mi> <mo>&lt;</mo> <mi>n</mi> </mrow> </math></EquationSource> </InlineEquation>, of this polynomial. In an attempt to obtain an integral setting of the inequalities concerning derivatives of this class of polynomials <i>p</i>(<i>z</i>), we have been able to establish extensions and generalizations of the above Ankeny and Rivlin’s inequality to integral analogs. As a consequence of our result, we obtained an improvement of the result due to Jain [Turk. J. Math., 31 (2007), <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="54" /> </InlineMediaObject> <EquationSource Format="TEX">\(89-94\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>89</mn> <mo>-</mo> <mn>94</mn> </mrow> </math></EquationSource> </InlineEquation>] which we have also compared by considering an example. Further, it is worth to note that we have compared our results by means of this numerical example where the bounds that are in terms of integral means are estimated numerically by numerical integration using Simpson’s <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1197_Article_IEq7.gif" Format="GIF" Height="26" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(\frac{1}{3}^{rd}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mfrac> <mn>1</mn> <mn>3</mn> </mfrac> <mrow> <mi mathvariant="italic">rd</mi> </mrow> </msup> </math></EquationSource> </InlineEquation> rule and illustrate graphically the obtained inequalities as regards sharpness.</p>

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New integral extensions of Ankeny and Rivlin’s inequality for the derivatives of the polynomial

  • Nirmal Kumar Singha,
  • Barchand Chanam

摘要

A well-known theorem due to Ankeny and Rivlin states that if p(z) is a polynomial of degree n such that p(z) has no zero in \(|z|<1\) | z | < 1 , then \(\begin{aligned} \max _{|z|=R\ge 1}|p(z)|\le \left( \frac{R^{n}+1}{2}\right) \max _{|z|=1}|p(z)|. \end{aligned}\) max | z | = R 1 | p ( z ) | R n + 1 2 max | z | = 1 | p ( z ) | . This research investigates the polynomial p(z) ensuring it possesses no zero in \(|z|<k\) | z | < k where \(k\ge 1\) k 1 . Simultaneously, we explore the \(s^{th}\) s th derivative, where \(0\le s<n\) 0 s < n , of this polynomial. In an attempt to obtain an integral setting of the inequalities concerning derivatives of this class of polynomials p(z), we have been able to establish extensions and generalizations of the above Ankeny and Rivlin’s inequality to integral analogs. As a consequence of our result, we obtained an improvement of the result due to Jain [Turk. J. Math., 31 (2007), \(89-94\) 89 - 94 ] which we have also compared by considering an example. Further, it is worth to note that we have compared our results by means of this numerical example where the bounds that are in terms of integral means are estimated numerically by numerical integration using Simpson’s \(\frac{1}{3}^{rd}\) 1 3 rd rule and illustrate graphically the obtained inequalities as regards sharpness.