1. Circles Objective: SWBAT define a circle and name its parts.
SWBAT use formulas to find the
circumference and area of a
circle.

2. Vocabulary
Circle a 2-dimensional shape made by drawing a
curve that is always the same distance
from a center
Radius the distance from the center to the edge
of a circle
Diameter a straight line going through the center of
a circle
Chord a straight line connecting 2 points on a
curve
Arc part of the circumference (edge) of a circle
Tangent a line that touches a curve at one point,
without cutting across it

3. Center the middle point of a circle
Sector a “pie slice” part of a circle
Segment an area of a circle made by a line and
an arc
Circumference the distance around the edge of a
circle
Area the amount of space inside a 2-
dimensional object

4. Formulas:
Circumference C = pi × diameter
C = d
Area of Circle A = pi × radius × radius
A = r2
 = 3.14

5. Label the different parts of this circle.
(arc, center, chord, circumference, diameter, radius, sector, segment, tangent)
Circumference
Segment
Chord
Tangent
Center
Arc
Diameter
Radius
Sector

6. Calculate the circumference of each of these circles
Calculate the circumference of each of these circles. Give your answers correct to two decimal places.
C = d
Radius = 5 ft
Diameter = =10
5 ft
3 in
C = 3.14 (3)
= 9.42 in
C = 3.14 (10)
= 31.4 ft

7. Calculate the area of each of these circles
Calculate the area of each of these circles. Give your answers correct to two decimal places.
A = r2
Diameter = 8 ft
Radius = 8 ÷ 2 =4
2 in
8 ft
A = 3.14 (2)2
= 3.14 (4)
A = in2
A = 3.14 (4)2
= 3.14 (16)
= ft2