Spring 2007 Mrs. Bubello

Circumference

Spring 2007 Mrs. Bubello

Circumference

Objectives

To identify the parts of a circle.

To derive a formula for circumference.

Spring 2007 Mrs. Bubello

Circumference

A circle is the set of all points in a plane that are the same distance from a given point, called the center of the circle.

Spring 2007 Mrs. Bubello

Circumference

The diameter is a segment that passes through the center of a circle.

Spring 2007 Mrs. Bubello

Circumference

The radius is a segment that has one endpoint at the center and the other point on the circle.

Spring 2007 Mrs. Bubello

Circumference

The ratio of every circle’s circumference to its diameter is the same.It has a special symbol, π, which is pronounced “pie”.

The circumference is the distance around a circle.

Spring 2007 Mrs. Bubello

Circumference

If you multiply by both sides of the equation by d, you get C = πd.

Pi (π) is about 3.14 or 22/7.

Since pi equals the ratio of the circumference and diameter. C/d = π.

Spring 2007 Mrs. Bubello

Circumference• The Egyptians and the Babylonians knew about the existence of the constant ratio pi.

• They didn’t know the value as we know it today.

• The Babylonians had an approximation of pi = 3 1/8 = 3.125.

• The Egyptians had a somewhat worse approximation of pi = 4*(8/9)^2 = 3.160484.