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Perimeter, Circumferenceand Area
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Perimeter and Circumference
Perimeter : The distance around a geometric figure.
Circumference: The distance around a circle.
Perimeter
To find perimeter add the lengths of all the sides.
– Example: Find the perimeter of the polygon
8 in
6 in
8 in
6 in
P = 8 + 8 + 6 + 6
P = 28
The perimeter is 28 in
Perimeter
– Example : Find the perimeter of the triangle
12 in
12 in
16 in
P = 12 + 12 + 16
P = 40
The perimeter is 40 in
Your Turn…. Find the perimeter
pg. 426 #1-3 ( 3 minutes) Make sure that there are no naked numbers.1. P = 6 + 4 + 8 P = 18m2. P = 7 + 5 + 5 + 7 P = 24in3. P = 8 + 8 + 8 + 8 P = 32 ft
Circumference
To find the circumference multiply times diameter, where is 3.14
C = d
Diameter
Definitions
Diameter (d): a line that passes through the center of a circle
Radius (r): half the diameter
d = 20, then r = 10 r = 15, then d = 30
Circumference
Example: Find the circumference
Diameter = 8 in
Circumference = d
C = 3.14(8)
C = 25.12
The circumference is 25.12 in
Circumference
Example: Find the circumference
radius = 10 cm
Circumference = d
Diameter = 2r = 2 (10) = 20
C = 3.14(20)
C = 62.8
The circumference is 62.8 cm
Your Turn…. Find the circumference
pg. 426 # 7-9 No naked numbers.7. C = d 8. C = d C = 3.14(12) C = 3.14(3) C = 37.7m C = 9.4 ft
9. C = d C = 3.14 (16) C = 50. 2 in
Area of Rectangles
The area of a rectangle is the product of its length and width.
A = ω
ω
Area of Rectangles
Find the area of the rectangle
10 ft
7.5 in
A = ω A = 10(7.5) A = 75 ft²
The area is 75 ft²
Area of Triangles
The area of a triangle is half the product of its base b and its height h.
A = bh
height
base
21
Area of Triangles
Example: Find the area of the triangle
21
6 in
5 in
A = bh
A = 5(6)
A = 15 in²
21
Area of Circles
The area of a circle is the product of and the square of the circle’s radius r.
A = r²
radius
Area of Circles
Example: Find the area of the circle
r = 3 m
A = r²A = 3.14(3)²A = 3.14(9)A = 28.26 m²The area of the circle is 28.26m²
Area of Circles
d = 8 in
A = r²Radius = 4 inA = 3.14(4)²A = 3.14(16)A = 50.24 in²
The area of the circle is 50.24in²
Lets Review
Perimeter = Sum of all sides
Circumference = d
Area of a Rectangle = ω
Area of a Triangle = bh
Area of a Circle = r²
21
