Lower and upper bounds of integral mean estimate for polar derivative of a polynomial

If p(z) is a polynomial of degree n having all its zeros in $|z|\leq k$, $k\geq1$, then for $r\geq 1$, Aziz [J. Approx. Theory, 55 (1988), 232-239] proved \begin{equation*} \left\lbrace\int\limits_{0}^{2\pi}|1+k^ne^{i\theta}|^{r}d\theta\right\rbrace^{\frac{1}{r}}\max_{|z|=1}|p'(z)|\geq n\left\lbrace\int\limits_{0}^{2\pi}|p(e^{i\theta})|^{r}d\theta\right\rbrace^{\frac{1}{r}}, \end{equation*} whereas, Devi et al. [Note Mat., 41 (2021), 19{29] proved that if p(z) is a polynomial of degree n having no zero in |z| k; k 1, then for r 0, \begin{equation*} k^{n}n\left\lbrace\int\limits_{0}^{2\pi}|p(e^{i\theta})|^{r}d\theta\right\rbrace^{\frac{1}{r}} \leq \left\lbrace\int\limits_{0}^{2\pi}|e^{i\theta}+k^n|^{r}d\theta\right\rbrace^{\frac{1}{r}}\left\{n\max_{|z|=1}|p(z)|-\max_{|z|=1}|p'(z)|\right\}, \end{equation*} provided jp0(z)j and jq0(z)j attain their maxima at the same point on jzj = 1, where $q(z)=z^{n}\overline{p\left(\frac{1}{\bar z}\right)}$. In this paper, we not only obtain improved extensions of the above inequalities into polar derivative by involving the leading coecient and the constant term of the polynomial but also give generalized integral extension of inequalities on polar derivative recently proved by Singh et al. [Complex Anal. Synerg., 9:3 (2023), 1-8].

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Publication Details

Journal
Annals of the University of Craiova Mathematics and Computer Science Series
Published
2024-12-25
DOI
https://doi.org/10.52846/ami.v51i2.1880
Citations
2
Primary Topic
Mathematical functions and polynomials
Type
article
Field-Weighted Citation Impact
1.95
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article

Lower and upper bounds of integral mean estimate for polar derivative of a polynomial

Sachin Kumar, Thoudam Ranaranjan, Chanam Barchand
2 citations
Annals of the University of Craiova Mathematics and Computer Science Series
Mathematical functions and polynomials
1.95
article

Lower and upper bounds of integral mean estimate for polar derivative of a polynomial

Sachin Kumar, Thoudam Ranaranjan, Chanam Barchand
article en
2 citations

Abstract

If p(z) is a polynomial of degree n having all its zeros in $|z|\leq k$, $k\geq1$, then for $r\geq 1$, Aziz [J. Approx. Theory, 55 (1988), 232-239] proved \begin{equation*} \left\lbrace\int\limits_{0}^{2\pi}|1+k^ne^{i\theta}|^{r}d\theta\right\rbrace^{\frac{1}{r}}\max_{|z|=1}|p'(z)|\geq n\left\lbrace\int\limits_{0}^{2\pi}|p(e^{i\theta})|^{r}d\theta\right\rbrace^{\frac{1}{r}}, \end{equation*} whereas, Devi et al. [Note Mat., 41 (2021), 19{29] proved that if p(z) is a polynomial of degree n having no zero in |z| k; k 1, then for r 0, \begin{equation*} k^{n}n\left\lbrace\int\limits_{0}^{2\pi}|p(e^{i\theta})|^{r}d\theta\right\rbrace^{\frac{1}{r}} \leq \left\lbrace\int\limits_{0}^{2\pi}|e^{i\theta}+k^n|^{r}d\theta\right\rbrace^{\frac{1}{r}}\left\{n\max_{|z|=1}|p(z)|-\max_{|z|=1}|p'(z)|\right\}, \end{equation*} provided jp0(z)j and jq0(z)j attain their maxima at the same point on jzj = 1, where $q(z)=z^{n}\overline{p\left(\frac{1}{\bar z}\right)}$. In this paper, we not only obtain improved extensions of the above inequalities into polar derivative by involving the leading coecient and the constant term of the polynomial but also give generalized integral extension of inequalities on polar derivative recently proved by Singh et al. [Complex Anal. Synerg., 9:3 (2023), 1-8].

Annals of the University of Craiova Mathematics and Computer Science SeriesVol. 51(2)
National Institute of Technology Manipur (IN)
Openalex Percentile: Top 12%
Mathematical functions and polynomials
1.95
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