1. Circles

2. Circle A has its center at point A.
All the points that make up circle A are the same distance from point A. A

3. AB is a radius of circle A. A circle has an infinite number of radii.
A radius is a line segment that has one endpoint on the circle and one endpoint at the center. A
AB is a radius of circle A.
A circle has an infinite number of radii.
All radii of a circle have the same length. B

4. A chord is a line segment joining any two points on a circle.
DB is a chord of circle A.
A circle has an infinite number of chords. B D

5. A diameter is a chord that passes through the center of a circle.
BC is a diameter of circle A.
A circle has an infinite number of diameters.
The length of the diameter is 2 times the length of the radius. B C

6. To find the circumference:
The circumference of a circle is its perimeter.
To find the circumference:
Let C = circumference, π (Pi) = 3.14, d = diameter, and r = radius.
C = πd or C = 2πr
C = 2πr
= 2 • 3.14 • 5
= 31.4 inches
C = πd
= 3.14 • 10 A B
5 inches C
10 inches

7. To find the area of a circle:
The area of a circle is the number of square units inside the circle.
To find the area of a circle:
Let A = area, π (Pi) = 3.14, and r = radius.
A = πr2
A = πr2
= 3.14 • 52
= 3.14 • 25
= 78.5 in2 B C
5 inches

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