# Pi 是永恆 (二)

$p \le C \le P$

$2nb \le C \le 2nB$

$2nR\sin[360/(2n)] \le C \le 2nR\tan[360/(2n)]$

$n\sin(180/n) \le C/(2R) \le n\tan(180/n)$

$\lim_{n\to\infty} n\sin(180/n) \le C/(2R) \le \lim_{n\to\infty} n\tan(180/n)$

$\lim_{n\to\infty} n\sin(180/n) = \lim_{n\to\infty} 180 \times \sin(180/n)/(180/n)$

$\lim_{n\to\infty} n\tan(180/n) = \lim_{n\to\infty} 180 \times \tan(180/n)/(180/n)$

$180 \le C/(2R) \le 180$

$\pi = C/(2R) = 180$ 度，

$\pi$是永恆。

Pi 是永恆 (一)》- 余海峯

## By David Yu

David Yu is the father of Simba and an Astrophysicist. He obtained his PhD in Astrophysics from the Max Planck Institute of Extraterrestrial Physics, Germany. He was formerly a postdoc at the KTH Royal Institute of Technology, Sweden, and is currently a lecturer at the University of Hong Kong. He served as the host of the RTHK TV31 programme Science Night, the Depute Editor-in-Chief of the Taiwanese Science Magazine Physics Bimonthly, and the Science Consultant of Stand News. The books he authored include Dr David’s 21 Mysteries of The Universe (2021), Space – A Down-to-Earth Astrophysicist (2021), Time – A Spacetime Journey of Astronomy and Physics (2019), and Secrets from the Stars (2017).