Question #107108
Construct an entire function f in complex with simple zeros at an = n^(1/2) for n belongs to natural numbers and no other zeros
1
Expert's answer
2020-03-30T12:51:03-0400

By the Weierstrass factorizaion theorem we obtain that f(z)=n=1En(zan)f(z)=\prod\limits_{n=1}^{\infty}E_n\left(\frac{z}{a_n}\right) is a entire function, such that {z:f(z)=0}={an}nN\{z: f(z)=0\}=\{a_n\}_{n\in\mathbb N}, and these zeros are simple, where En(z)=(1z)exp(k=1nzkk)E_n(z)=(1-z)\exp\left(\sum\limits_{k=1}^n \frac{z^k}{k}\right)

Indeed

1) limnan=+\lim\limits_{n\to\infty}|a_n|=+\infty

2)For every r>0r>0 there is NN such that ran<12\left|\frac{r}{a_n}\right|<\frac{1}{2} for all n>Nn>N, thenn=1rann+1=n=1Nrann+1+n=N+1rann+1\sum\limits_{n=1}^{\infty}\left|\frac{r}{a_n}\right|^{n+1}=\sum\limits_{n=1}^N\left|\frac{r}{a_n}\right|^{n+1}+\sum\limits_{n=N+1}^{\infty}\left|\frac{r}{a_n}\right|^{n+1}\le

n=1Nrann+1+n=N+1(12)n+1\le\sum\limits_{n=1}^N\left|\frac{r}{a_n}\right|^{n+1}+\sum\limits_{n=N+1}^{\infty}\left(\frac{1}{2}\right)^{n+1}, so n=1ranpn+1\sum\limits_{n=1}^{\infty}\left|\frac{r}{a_n}\right|^{p_n+1} , where pn=np_n=n, is convergent series.

Then f(z)=n=1Epn(zan)=n=1En(zan)f(z)=\prod\limits_{n=1}^{\infty}E_{p_n}\left(\frac{z}{a_n}\right)=\prod\limits_{n=1}^{\infty}E_n\left(\frac{z}{a_n}\right) is a entire function with simple zeros {an}nN\{a_n\}_{n\in\mathbb N}.

Answer: f(z)=n=1En(zan)=n=1En(zn)f(z)=\prod\limits_{n=1}^{\infty}E_n\left(\frac{z}{a_n}\right)=\prod\limits_{n=1}^{\infty}E_n\left(\frac{z}{\sqrt{n}}\right), where En(z)=(1z)exp(k=1nzkk)E_n(z)=(1-z)\exp\left(\sum\limits_{k=1}^n \frac{z^k}{k}\right)


Need a fast expert's response?

Submit order

and get a quick answer at the best price

for any assignment or question with DETAILED EXPLANATIONS!

Comments

No comments. Be the first!
LATEST TUTORIALS
APPROVED BY CLIENTS