Objective: Find the circumference and area of circles
Mar 27, 2015
Objective: Find the circumference and area of circles
Circle – Label The parts
Radius
Diameter
Circumference: C=2 rC=2 r
• Circumference is the length of the distance AROUND the circle
• Take 2 times the radius and pi
Circumference: C=2∏r
• Find the circumference of a circle with radius 5.
• Find the circumference of a circle with diameter 10.C r
C
C
C
C inches
2
2
1 0
1 0 3 1 4
3 1 4
(5)
( . )
.
5 in.C rorC d
C
C
C
C inches
2
1 0
1 0
1 0 3 1 4
3 1 4
( )
( . )
.
10 in.
Circumference
• Find the circumference of a circle with radius 2.
• Find the circumference of a circle with diameter 8.
C r 2
Area of a Circle
• AreaArea of a circle is the amount of space the circle covers.
A r 2
Area of a Circle
• Find the area of a circle with radius 9.
A r 2
A r
A
A
A
A
2
29
8 1
8 1 3 1 4
2 5 4 3 4
( )
( . )
.
9 feet
Find the area of the circles below. Use 3.14. 1) 2)
6 in.
2A r2A (6)
A 36A 36 A 36 (3.14)
2A 113.04 in
16 m
2A r2A (16)
A 256A (3.14) 256
2A 803.84 in
Area of a Circle
• Find the area of a circle with radius 5.
A r 2
Area of a Circle
• Find the area of a circle with diameter 24.
A r 2
Instructional ConversationInstructional Conversation
Problem #1Problem #1
What is the formula for circumference?
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Problem #2Problem #2• Find the circumference.
4
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Problem #3Problem #3
What is the formula for area of a circle?
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Problem #4Problem #4• Find the area.
20