Suppose $f:D(0,1) \longrightarrow \mathbb{C}$ is holomorphic, where $D(0,1) = \{z \in \mathbb{C} \mid |z|<1\},$ and assume the maximum $|f(z)| \le 2$.
Estimate: $|f^{(3)}(i/3)|$.
I have the solution to this problem which used $R=2/3$.
I am not sure how to find this $R$ because I don't understand the Cauchy Estimate that well. Any help to understand this problem will be real helpful thank you.