I could not prove below theorem. can you help me ?
Thm : let $f(z)$ be analytic in $|z|<1$ with $f(0)=0$ and $\left|f(z)\right|\le 1$ for all $z$, $|z|<1$. prove that $\left|f''(0)\right|\le2$
Thanks
I could not prove below theorem. can you help me ?
Thm : let $f(z)$ be analytic in $|z|<1$ with $f(0)=0$ and $\left|f(z)\right|\le 1$ for all $z$, $|z|<1$. prove that $\left|f''(0)\right|\le2$
Thanks