Algebra: Chapter 9 TEST
Math-8: Chapter 7-4, p 341
Circles and Circumference
Definitions:
- The circumference of a circle is the distance around the perimeter, just like a rectangle. We don’t call it the perimeter but the circumference.
- The diameter is the distance across the circle through the center.
- A radius is the distance from the center of the circle to the edge. The radius is 1/2 of the diameter or 2*radius = diameter.
- π is the greek letter for the ratio of the circumference ÷ diameter.
The circumference formula, given c, is then `c=πd` or, since `d=2r`, or `c=2πr`.
π has the value 3.141592654, we commonly use 3.14. Another approximation when we work with fractions is 22/7.
Finally, since `c=πd`, then `d=c/π` and since `c=2πr`, then `r=c/(2π)`.