Finding the Center of A Circle

Larry Stroud — Thu, 02 Sep 2010 19:19:25 +0000

Thales Theorem is the basis for a simple method for locating the center of a circle using a carpenter’s square as follows:

1. Place the corner of the carpenter’s square anywhere on the circumference and position the “legs” of the square so they both intersect the circumference. Mark the points on the circumference where the legs intersect the circumference. Then draw a line connected the two marked points. This will be a diameter.

2. Repeat Step 1 but move the corner of the carpenter’s square to another point on the circumference.

3. The center of the circle will be located at the intersection of the two diameters.

This is illustrated in the following graphic:

A Better Approximation for PI

Larry Stroud — Fri, 16 Jul 2010 21:25:57 +0000

Many students know that 22/7 is a common fraction that is approximately equal to PI and is accurate to 2 decimal places. However, a better common fraction approximation to PI is 355/113 which is accurate to 6 decimal places. This fraction also easy to remember by writing the digits 113355 and dividing the last 3 digits by the first 3 digits.