
The following theorem is proven: Let F ( z ) F(z) be convex and univalent in Δ = { z : | z | > 1 } , F ( 0 ) = 1 \Delta = \{ z:|z| > 1\} ,F(0) = 1 . Let f ( z ) f(z) be analytic in Δ , f ( 0 ) = 1 , f ′ ( 0 ) = … = f ( n − 1 ) ( 0 ) = 0 \Delta ,f(0) = 1,f’(0) = \ldots = {f^{(n - 1)}}(0) = 0 , and let f ( z ) ≺ F ( z ) f(z) \prec F(z) in Δ \Delta . Then for all γ ≠ 0 \gamma \ne 0 , Re γ ⩾ 0 \gamma \geqslant 0 , \[ γ z − γ ∫ 0 z τ γ − 1 f ( τ ) d τ ≺ γ z − γ / n ∫ 0 z 1 / n τ γ − 1 F ( τ n ) d τ . {\gamma _z}^{ - \gamma }\int _0^z {{\tau ^{\gamma - 1}}f(\tau )d\tau \prec \gamma {z^{ - \gamma /n}}\int _0^{{z^{1/n}}} {{\tau ^{\gamma - 1}}F({\tau ^n})d\tau .} } \] This theorem, in combination with a method of D. Styer and D. Wright, leads to the following Corollary. Let f ( z ) , g ( z ) f(z),g(z) be convex univalent in Δ , f ( 0 ) = f ( 0 ) = g ( 0 ) = g ( 0 ) = 0 \Delta ,f(0) = f(0) = g(0) = g(0) = 0 . Then f ( z ) + g ( z ) f(z) + g(z) is starlike univalent in Δ \Delta . Other applications of the theorem are concerned with the subordination of f ( z ) / z f(z)/z where f ( z ) f(z) belongs to certain classes of convex univalent functions.
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), Extremal problems for conformal and quasiconformal mappings, other methods
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), Extremal problems for conformal and quasiconformal mappings, other methods
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