Toronto Math Forum

MAT334-2018F => MAT334--Lectures & Home Assignments => Topic started by: ashley on December 04, 2018, 11:17:07 PM

Title: 3.2 Q7
Post by: ashley on December 04, 2018, 11:17:07 PM
I have no ideas how to start this question. Can someone help me to solve? Thank you.
Title: Re: 3.2 Q7
Post by: Kris on December 04, 2018, 11:26:11 PM
The function $h(z)=e^{F(z)}$ is analytic on the disc $\{\mid$$z$-$z_0\mid$$\leq$$r\}$, it never equals zero, and $\mid$$h(z_0)\mid=1$.
Hence the maximum and the minimum are attained on the boundary circle $\{\mid$$z$-$z_0\mid$$=r\}$.
Let $z_{max}$, $z_{min}$ be the corresponding points, so $1<\mid$$h(z_{max})\mid$=$e^{Re(z_{max})}$, $1>\mid$$h(z_{min})\mid$=$e^{Re(z_{min})}$.
We deduce that Re($f(z_{max})$)$>0>Re(f(z_{min}))$