1. Perimeter and Circumference
9-2
Perimeter and Circumference
Course 2
Warm Up
Problem of the Day
Lesson Presentation

2. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Warm Up
Add or multiply.
3. 22 · 3.14
27.6
37.5
69.08

3. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Problem of the Day
A rectangular piece of sheet metal measures 5 in. by 6 in. A rectangular notch 1 in. deep and in. wide is cut 7 64
out of the middle of each side. What is
the perimeter of the piece after the
cuts have been made? (Hint: You don’t
have to use fractions.)
30 in. (the original 6 in. by 5 in. sheet
plus 8 in. for the eight 1 in. cuts)

4. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Learn to find the perimeter of a polygon and the circumference of a circle.

5. Insert Lesson Title Here
Course 2
9-2
Perimeter and Circumference
Insert Lesson Title Here
Vocabulary
perimeter
circumference

6. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
The distance around a geometric figure is its perimeter. To find the perimeter P of a polygon, you can add the lengths of its sides.

7. Additional Example 1: Finding the Perimeter of a Polygon
Course 2
9-2
Perimeter and Circumference
Additional Example 1: Finding the Perimeter of a Polygon
Find the perimeter.
25 cm
25 cm
15 cm
P =
Use the side lengths.
P = 65
Add.
The perimeter of the triangle is 65 cm.

8. Insert Lesson Title Here
Course 2
9-2
Perimeter and Circumference
Insert Lesson Title Here
Check It Out: Example 1
Find the perimeter of the polygon.
20 cm
25 cm
30 cm
P =
Use the side lengths.
P = 75
Add.
The perimeter of the triangle is 75 cm.

9. PERIMETER OF A RECTANGLE
Course 2
9-2
Perimeter and Circumference
PERIMETER OF A RECTANGLE
P = 2l + 2w
The perimeter P of a rectangle is the sum of twice its length l and twice its width w. w l

10. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Additional Example 2: Using Properties of a Rectangle to Find Perimeter
Find the perimeter of a rectangle.
14 ft
18 ft
P = 2l + 2w
Use the formula.
P = (2 · 18) + (2 ·14)
Substitute for l and w.
P =
Multiply.
P = 64
Add.
The perimeter of the rectangle is 64 ft.

11. Insert Lesson Title Here
Course 2
9-2
Perimeter and Circumference
Insert Lesson Title Here
Check It Out: Example 2
Find the perimeter of a rectangle.
16 ft
8 ft
P = 2l + 2w
Use the formula.
P = (2 · 8) + (2 · 16)
Substitute for l and w.
P =
Multiply.
P = 48
Add.
The perimeter of the rectangle is 48 ft.

12. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference C d
The distance around a circle is called circumference. For every circle, the ratio of circumference C to diameter d is the same. This ratio, , is
represented by the Greek letter , called pi. Pi is approximately equal to 3.14 or By solving the 22 7
equation =  for C, you get the formula for circumference. the formula for circumference.
C = d, or C = 2r.

13. CIRCUMFERENCE OF A CIRCLE
Course 2
9-2
Perimeter and Circumference
CIRCUMFERENCE OF A CIRCLE
The circumference C of a circle is  times the diameter d, or 2 times the radius r.
Radius
C = d, or C = 2r
Diameter
Circumference

14. Additional Example 3A: Finding the Circumference of a Circle
Course 2
9-2
Perimeter and Circumference
Additional Example 3A: Finding the Circumference of a Circle
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = d
You know the diameter.
12 in.
C  3.14 · 12
Substitute for  and d.
C  37.68
Multiply.
The circumference of the circle is about 37.7 in.

15. Additional Example 3B: Finding the Circumference of a Circle
Course 2
9-2
Perimeter and Circumference
Additional Example 3B: Finding the Circumference of a Circle
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = 2r
You know the radius.
18 cm
C  2 · 3.14 · 18
Substitute for  and r.
C 
Multiply.
The circumference of the circle is about cm.

16. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Check It Out: Example 3A
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = d
You know the diameter.
7 in.
C  3.14 · 7
Substitute for  and d.
C  21.98
Multiply.
The circumference of the circle is about 22.0 in.

17. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Check It Out: Example 3B
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = 2r
You know the radius.
11 cm
C  2 · 3.14 · 11
Substitute for  and r.
C  69.08
Multiply.
The circumference of the circle is about 69.1 cm.

18. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
If the diameter or radius of a circle is a
multiple of 7, use for p.
Helpful Hint
22 7

19. Additional Example 4: Application
Course 2
9-2
Perimeter and Circumference
Additional Example 4: Application
The diameter of a circular pond is 42 m. What is its circumference? Use
for . 22 7
C = d
You know the diameter. 22 7 22 7
C 
· 42
Substitute
for  and 42 for d. 22 7 42 1
C 
Write 42 as a fraction. 6 22 7 42 1
C 
Simplify. 1
C  132
Multiply.
The circumference of the pond is about 132 m.

20. Perimeter and Circumference
Course 2
9-2
Perimeter and Circumference
Check It Out: Example 4
The diameter of a circular spa is 14 m. What is its circumference? Use 22 7
for .
C = d
You know the diameter. 22 7 22 7
C 
· 14
Substitute
for  and 14 for d. 22 7 14 1
C 
Write 14 as a fraction. 2 22 7 14 1
C 
Simplify. 1
C  44
Multiply.
The circumference of the spa is about 44 m.

21. Perimeter and Circumference Insert Lesson Title Here
Course 2
9-2
Perimeter and Circumference
Insert Lesson Title Here
Lesson Quiz
Find the perimeter.
3. What is the circumference of a circle with a
a radius of 8 inches? Use 3.14 for .
4. If a guardrail is to be placed around the edge
of a circular swimming pool with a diameter of
21 ft, how many feet of railing will be needed?
8 m
12 m
8 in.
10 m
45 m
36 in.
9 m
6 m
10 in.
50.24 in.
Use for . 22 7
66 ft