Day 85

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)`.

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