Some Results of The Class of Functions with Bounded Radius Rotation

Abstract

Let $\mathcal{A}$ be the family of functions $f(z)=z+a_2z^2+...$ which are analytic in the open unit disc $\mathbb{D}=\{z: |z|<1 \}$, and denote by $\pe$ of functions $p(z)=z+p_1z+p_2z^2+...$ analytic in $\de$ such that $p(z)$ is in $\pe$ if and only if $$p(z)\prec \frac{1+z}{1-z} \Leftrightarrow p(z)=\frac{1+\phi(z)}{1-\phi(z)}, $$ for some Schwarz function $\phi(z)$ and every $z\in\de.$ Let $f(z)$ be an element of $\mathcal{A}$, and satisfies the condition $$z\frac{f'(z)}{f(z)}=\left(\frac{k}{4}+\frac{1}{2}\right)p_{1}(z)-\left(\frac{k}{4}-\frac{1}{2}\right)p_{2}(z)$$ where $p_1(z), p_2(z)\in \pe$ and $k\geq 2$, then $f(z)$ is called function with bounded radius rotation. The class of such functions is denoted by $R_k$. This class is generalization of starlike functions. The main purpose is to give some properties of the class $R_k$.