Holt CA Course 1 9-4 Circumference and Area MG2.1 Use formulas routinely for finding the perimeter and area of basic two-dimensional figures and the surface area and volume of basic three- dimensional figures, including rectangles, parallelograms, trapezoids, squares, triangles, circles, prisms, and cylinders. Also covered: MG3.2 California Standards
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Holt CA Course 1
9-4 Circumference and Area
MG2.1 Use formulas routinely for finding the perimeter and area of basic two-dimensional figures and the surface area and volume of basic three-dimensional figures, including rectangles, parallelograms, trapezoids, squares, triangles, circles, prisms, and cylinders.
Also covered: MG3.2
California
Standards
Holt CA Course 1
9-4 Circumference and Area
Radius
CenterDiameter
Circumference
The diameter d is twice the radius r.
dd = 2= 2rr
The circumference of a circle is the distance around the circle.
Holt CA Course 1
9-4 Circumference and Area
Holt CA Course 1
9-4 Circumference and Area
Remember!Pi () is an irrational number that is often
approximated by the rational numbers 3.14
and .227
Holt CA Course 1
9-4 Circumference and AreaAdditional Example 1: Finding the Circumference of a
Circle
A. circle with a radius of 4 m
C = 2r= 2(4)
= 8m 25.1 m
B. circle with a diameter of 3.3 ft
C = d= (3.3)= 3.3ft 10.4 ft
Find the circumference of each circle, both in terms of and to the nearest tenth. Use 3.14 for .
Holt CA Course 1
9-4 Circumference and AreaCheck It Out! Example 1
A. circle with a radius of 8 cm
C = 2r= 2(8)
= 16cm 50.2 cm
B. circle with a diameter of 4.25 in.
C = d= (4.25)
= 4.25in. 13.3 in.
Find the circumference of each circle, both in terms of and to the nearest tenth. Use 3.14 for .
Holt CA Course 1
9-4 Circumference and Area
Holt CA Course 1
9-4 Circumference and AreaAdditional Example 2: Finding the Area of a Circle
A = r2 = (42)= 16in2 50.2 in2
A. circle with a radius of 4 in.
Find the area of each circle, both in terms of and to the nearest tenth. Use 3.14 for .
B. circle with a diameter of 3.3 m
A = r2 = (1.652)
= 2.7225 m2 8.5 m2
d2 = 1.65
Holt CA Course 1
9-4 Circumference and Area
B. circle with a diameter of 2.2 ft
A = r2 = (1.12)
= 1.21ft2 3.8 ft2
d2 = 1.1
Check It Out! Example 2
Find the area of each circle, both in terms of and to the nearest tenth. Use 3.14 for .
A = r2 = (82)
= 64cm2 201.0 cm2
A. circle with a radius of 8 cm
Holt CA Course 1
9-4 Circumference and AreaAdditional Example 3: Finding the Area and
Circumference on a Coordinate Plane
A = r2
= (32)
= 9units2
28.3 units2
C = d
= (6)
= 6units
18.8 units
Graph the circle with center (–2, 1) that passes through (1, 1). Find the area and circumference, both in terms of and to the nearest tenth. Use 3.14 for
Holt CA Course 1
9-4 Circumference and AreaCheck It Out! Example 3
x
yA = r2
= (42)
(–2, 1)
= 16units2
50.2 units2
C = d
= (8)
= 8units
25.1 units
4
(–2, 5)
Graph the circle with center (–2, 1) that passes through (–2, 5). Find the area and circumference, both in terms of and to the nearest tenth. Use 3.14 for
Holt CA Course 1
9-4 Circumference and AreaAdditional Example 4: Measurement Application
C = d = (56)
176 ft (56) 22 7
22 7
A Ferris wheel has a diameter of 56 feet and makes 15 revolutions per ride. How far
would someone travel during a ride? Use for .
Find the circumference.
56 1
22 7
The distance is the circumference of the wheel times the number of revolutions, or about 176 15 = 2640 ft.
Holt CA Course 1
9-4 Circumference and Area
12
3
6
9
Check It Out! Example 4
A second hand on a clock is 7 in. long. What is
the distance it travels in one hour? Use for .
22 7
C = d = (14)
(14) 22 7
Find the circumference.
44 in.
The distance is the circumference of the clock times the number of revolutions, or about 44 60 = 2640 in.
14 1
22 7
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