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Integral mean estimates for the polar derivative of a polynomial

Complex Variables 2013-04-03 v1

Abstract

Let P(z) P(z) be a polynomial of degree n n having all zeros in zk|z|\leq k where k1,k\leq 1, then it was proved by Dewan \textit{et al} that for every real or complex number α\alpha with αk|\alpha|\geq k and each r0r\geq 0 n(αk){02πP(eiθ)rdθ}1r{02π1+keiθrdθ}1rMaxz=1DαP(z). n(|\alpha|-k)\left\{\int\limits_{0}^{2\pi}\left|P\left(e^{i\theta}\right)\right|^r d\theta\right\}^{\frac{1}{r}}\leq\left\{\int\limits_{0}^{2\pi}\left|1+ke^{i\theta}\right|^r d\theta\right\}^{\frac{1}{r}}\underset{|z|=1}{Max}|D_\alpha P(z)|. \indent In this paper, we shall present a refinement and generalization of above result and also extend it to the class of polynomials P(z)=anzn+ν=μnanνznν,P(z)=a_nz^n+\sum_{\nu=\mu}^{n}a_{n-\nu}z^{n-\nu}, 1μn,1\leq\mu\leq n, having all its zeros in zk|z|\leq k where k1k\leq 1 and thereby obtain certain generalizations of above and many other known results.

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Cite

@article{arxiv.1302.7066,
  title  = {Integral mean estimates for the polar derivative of a polynomial},
  author = {N. A. Rather and Suhail Gulzar},
  journal= {arXiv preprint arXiv:1302.7066},
  year   = {2013}
}

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8 pages