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Four-point distortion theorem for complex polynomials. (English) Zbl 1300.30009

In the paper a result in connection with the distortion of the cross ratio of four points under the mapping defined by a complex polynomial with restricted critical values is proved. The corollaries deduced from this result include some inequalities which involve the absolute value and certain coefficients of a polynomial. In particular, the author obtains an exact lower bound for the maximum moduli of the critical values of a polynomial \(P\) of degree \(n\) which is normalized by the following conditions: i) the value of \(P\) at the origin is zero and ii) its derivative at the origin is non-zero.

MSC:

30C10 Polynomials and rational functions of one complex variable
30C35 General theory of conformal mappings
30C85 Capacity and harmonic measure in the complex plane

References:

[1] DOI: 10.1070/RM2012v067n04ABEH004803 · Zbl 1267.30012 · doi:10.1070/RM2012v067n04ABEH004803
[2] Goluzin GM, Geometric theory of functions of a complex variable, Translations of Mathematics Monographs (1969)
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[4] Dubinin VN, Math. Notes 92 pp 103– (2012)
[5] DOI: 10.1142/1284 · doi:10.1142/1284
[6] Hurwitz A, Vorlesungen über allgemeine Funktionentheorie und Elliptische Funktionen (1964) · doi:10.1007/978-3-642-49657-8
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[8] DOI: 10.1070/SM2006v197n08ABEH003793 · Zbl 1145.30003 · doi:10.1070/SM2006v197n08ABEH003793
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