1. Circles and Circumference

2. Definitions
Circle – the locus (set) of all points in a plane equidistant from a given point called the center.
A circle is usually named by the center point. D
Circle
Center Point

3. Definitions C Diameter – a chord that passes
through the center point. CE is a diameter F D
Radius – any segment with endpoints
that are the center and a point on the
circle. CF, EF, and DF are all radii. E

4. Some Important Facts! Diameter is twice the radius.
D = 2R
Radius is one-half the diameter
R = ½ D
Circumference is the distance around a circle.
C = d or C = 2r

5. Work this problem! The diameter of Circle X is 22 cm C =  D
C = (3.14)(22 cm)
C = cm = 69.1 cm

6. Work this problem Find the circumference of circle K.
To find circumference we need
either the diameter or radius. K 3
So, C = 2r
C = (2)(3)(3.14)
C = 18.8 units

7. An actual answer
on a geometry
test.