Math 149S. Capstone Mathematics for Teachers.
Homework 10
Consider a circle of radius 1. Its circumference is 2π.
- Use regular polygons to obtain a lower bound and an upper bound for the number π as follows.
- Inscribe a square into the circle. Find its perimeter. Let's denote this perimeter p1.
- Circumscribe a square. Find its perimeter. Let's denote this perimeter p2.
- Notice that p1 < 2π < p2. Divide everything by 2 to obtain an inequality for π:
p1/2 < π < p2/2.
- Repeat the above procedure with regular octagons. You will obtain another inequality.
- Repeat the above procedure with regular 16-gons. You will obtain one more inequality.
Notice that the more sides, the harder and longer calculations, but the better the estimate.
Remark: Archimedes used polygons with up to 96 sides.
This page was last revised on 12 April 2019.