How much fencing do we need for our pasture?

How much border do we need for our nursery?

Bessie got away

again!

Some shapes have specific formulas, but to find perimeter, just

add up all the sides!

Square Perimeter = 4s (s = side length)

Rectangle Perimeter = 2l + 2w (l = length and w = width)

Triangle Perimeter = s1 + s2 + s3 (the sides)

Ex 1: Find the perimeter of..

a. A square whose sides have length 8 cm.

8 cm

8 cm

8 cm8 cmP = 4sP = 4(8)P = 32 cm

b. A rectangle whose length is 5 m and width is 11 m.

5 m

11 m

P = 2l + 2wP = 2(5) + 2(11)P = 10 + 22P = 32 m

11 m

5 m

c. A triangle whose side lengths are 3 in, 4 in, and 5 in.

P = s1 + s2 + s3P = 3 + 4 + 5P = 12 in

3 in

4 in5 in

Ex 2: Find the indicated side length.

a. A square with perimeter 20 in.

5 in

5 in

5 in5 inP = 4s20 = 4s5 in = s

b. A rectangle with perimeter 30 ft and length 4 ft.

4 ft

11 ft

P = 2l + 2w30 = 2(4) + 2w30 = 8 + 2w22 = 2w11 = w

11 ft

4 ft

c. A triangle with perimeter 23 mm and remaining side lengths 8 mm and 9 mm.

P = s1 + s2 + s323 = 8 + 9 + s323 = 17 + s36 mm = s3

6 mm

9 mm

8 mm

Ex 3: Find the perimeter.8

64

5

2

Fill in the other lengths..

5 + 2 = 7

8 + 4 = 12

4

4

6

Perimeter = 8 + 6 + 4 + 7 + 12 + 2 + 4 + 5 + 4 + 6Perimeter = 58 units

How would you add up all the sides of a circle? A circle has no sides.

Circumference, C, is similar to Perimeter but is used with circles and

is defined differently.

A diameter is equivalent to 2 radii. Depending upon which piece is given,

use one of the following.

diameter

dC

or

rC

2

Ex 4: Find the circumference of a circle with radius .

38

38

316

)38(2

2

C

C

rC

Unless you are told to use 3.14, leave your answer in terms of pi.

Ex 5: A bicycle wheel has a diameter of 60 cm. How far will it travel if it makes 50 revolutions? Use π = 3.14.

●

The wheel spins…

● ● ●

50 times

Find circumference to determine how far the wheel moves with each spin. Multiply by 50 since it spins

50 times. C = πd = (3.14)(60) = 188.4Distance = 188.4 (50) = 9420 cm