On Bernstein and Turán-type integral mean estimates for polar derivative of a polynomial

Abstract

Abstract Let p ( z ) $p(z)$ be a polynomial of degree n having no zero in | z | < k $|z|< k$ , k ≤ 1 $k\leq 1$ , then Govil [Proc. Nat. Acad. Sci., 50(1980), 50-52] proved max | z | = 1 | p ′ ( z ) | ≤ n 1 + k n max | z | = 1 | p ( z ) | , $$ \max _{|z|=1}|p'(z)|\leq \frac{n}{1+k^{n}}\max _{|z|=1}|p(z)|, $$ provided | p ′ ( z ) | $|p'(z)|$ and | q ′ ( z ) | $|q'(z)|$ attain their maxima at the same point on the circle | z | = 1 $|z|=1$ , where q ( z ) = z n p ( 1 z ‾ ) ‾ . $$ q(z)=z^{n}\overline{p\bigg(\frac{1}{\overline{z}}\bigg)}. $$ In this paper, we present integral mean inequalities of Turán- and Erdös-Lax-type for the polar derivative of a polynomial by involving some coefficients of the polynomial, which refine some previously proved results and one of our results improves the above Govil inequality as a special case. These results incorporate the placement of the zeros and some coefficients of the underlying polynomial. Furthermore, we provide numerical examples and graphical representations to demonstrate the superior precision of our results compared to some previously established results.

Keywords

• Bernstein-type inequalities
• Tuŕan-type inequalities
• Polar derivative
• Integral inequalities