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Some Inequalities for the Polar Derivative of Some Classes of Polynomials

Complex Variables 2018-04-30 v1

Abstract

In this paper, we investigate an upper bound of the polar derivative of a polynomial of degree nn p(z)=(zzm)tm(zzm1)tm1(zz0)t0(a0+ν=μn(tm++t0)aνzν)p(z)=(z-z_m)^{t_m} (z-z_{m-1})^{t_{m-1}}\cdots (z-z_0)^{t_0}(a_0+\sum\limits_{\nu=\mu} ^{n-(t_m+\cdots+t_0)} a_{\nu}z^\nu) where zeros z0,,zmz_0,\ldots,z_m are in {z:z<1}\{z:|z|<1\} and the remaining n(tm++t0)n-(t_m+\cdots+t_0 ) zeros are outside {z:z<k}\{z:|z|<k\} where k1.k \geq 1. Furthermore, we give a lower bound of this polynomial where zeros z0,,zmz_0,\ldots,z_m are outside {z:zk}\{z:|z|\leq k\} and the remaining n(tm++t0)n-(t_m+\cdots+t_0 ) zeros are in {z:z<k}\{z:|z|<k\} where k1.k\leq 1.

Keywords

Cite

@article{arxiv.1804.10203,
  title  = {Some Inequalities for the Polar Derivative of Some Classes of Polynomials},
  author = {Nuttapong Arunrat and Keaitsuda Maneeruk Nakprasit},
  journal= {arXiv preprint arXiv:1804.10203},
  year   = {2018}
}

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17 pages