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LESSON 7.6AREA AND CIRCUMFERENCE OF CIRCLES
OBJECTIVE:To use formulas for the circumference and area of circles
DEFINITIONSis the set of all points that
is a given distance from a given point.
The given point is the of the circle.
CENTER
A CIRCLE
The given distance is the of the circle, which is a segment with one endpoint on the circle and the other at the center of the circle.
RADIUS
is a segment, with both endpoints on the circle, that passes through the center of the segment.
THE DIAMETER
One diameter equals two radii or d = 2r FORMULAS:
Area of a circle
Circumference of a circle
A = π r2
C = 2πr or C = πd
Find the circumference and the area.
Leave π in the answer. 15 in
C = πd
C = 15π in.
A = πr2
A = π(7.5)2
A = 56.25π in2
Example #1
10 m
C = 2πr A = πr2
C = 2(3.14)(10)
C = 62.8m
A = (3.14)(10)2
A = 314m2
Use 3.14 for π
Example #2
Find the circumference and the area.
Example #3If the circumference of a circle is 8π in., then find the area.
First, we must find the radius.
Then we will use the radius to find the area.
4 in = r
8 π = 2πr
8 π = 2πr 2π 2π
A = πr2
A = π(4)2
A = 16π in2
C = 2πr
Find the radius. Find the area.
Example #44. If the area of a circle is 113.04 m2, then find the circumference. Use 3.14 for π.
First, we must find the radius.
Then we will use the radius to find C
A = πr2
113.04 = (3.14)r2
36 = r2
6 m = r
C = 2πr
C = 2(3.14)(6)
C = 37.68m
Find the radius. Find Circumference
ASSIGNMENT:
7.6 Worksheet Show necessary work
Minimum 3 lines