How to describe a circle

MoebiusStripper writes about MathPower 12, an all-too-popular popular high-school mathematics textbook published by McGraw-Hill. In case the student doesn’t already know what a circle is, the text provides the following explanation:

The compact disc player is everywhere these days. Developed initially by Philips and Sony, it first came on the market in 1983. By 1986, over one million CD players were being sold each year. Because of the low-cost laser components, the CD player has become one of the most successful electronic devices to date.

If you trace around the outside of a CD, the result is a circle.

A circle is the set or locus of all points in a plane which are equidistant from a fixed point. This fixed point is called the centre. The distance from this centre to any point on the circle is called the radius.

There could be a lot of interesting problems about CDs, but no: this explanation serves purely to “motivate” the definitions of circle, center, and radius.

Categories: Math, Teaching & Learning