Perimeter of Composite Figures w/Circles

Perimeter of Composite

Figures with Circles

Let’s review circumference

Circumference is the perimeter of a
circle

Two formulas to find circumference:

C = πd

Or

C = 2πr

What happens if we need to find perimeter of this shape?

Multiple Select

What 2 shapes make up this figure?

• Circle

• Triangle

• Rectangle

• Square

A circle and a rectangle make up this figure.

Two semicircles make 1 whole circle

Two steps to find perimeter

1. Find circumference
2. Add in the other 2

sides

What does this look like?

1. Find circumference

C = πd

C = π x 5 = 15.71 ft

2. Add in the other 2 sides
3. 15.71 + 7 + 7 = 29.71 ft

Let's find perimeter of this figure.

Step 1:

Find Circumference -

C = πd

C = π x 4

C =

Multiple Choice

Complete the first step in finding perimeter of this figure.

Find circumference.

C = πd

C = π x 4

• 12.57 cm

• 12 cm

• 10.57 cm

• 15.57 cm

To find circumference....

Step 1:

Find Circumference -

C = πd

C = π x 4

C = 12.57 cm

Multiple Choice

Next, add the 2 sides to the circumference to calculate the total perimeter.

What is the perimeter?

12.57 + 7 + 7

• 20.57 cm

• 25 cm

• 29.57 cm

• 30 cm

Find Perimeter - the steps

Step 1:

Find Circumference -

C = πd

C = π x 4

C = 12.57 cm
Step 2 - add the other sides to circumference.
12.57 + 7 +7 = 29.57 cm

Let’s do that again - Find Perimeter by first finding Circumference.

Step 1:

Find Circumference -

C = πd

C = π x 4

C =

Multiple Choice

Step 1 - Find Circumference

C = πd

C = π x 4

• 40

• 12.57 in

• 12 in

• 10.57 in

Next, add the sides to the circumference. What is the perimeter?

Step 2 - add the sides to the
circumference.

12.57 + 5 + 5

Perimeter =

Multiple Choice

Next, add the other 2 sides to the circumference.

What is the total perimeter of this figure?

12.57 + 5 + 5

• about 20 in

• 2.57 in

• 12.57 in

• 22.57 in

What is the perimeter of this figure?

Remember the steps:

1. Find circumference

C = πd

C = π x 4 = _____

2. Add in the other 2 sides

Multiple Choice

What is the perimeter of this composite figure?

Remember:

Find circumference - C=πd

Then add the other 2 sides to the circumference.

• 28.57 m

• 27.57 m

• 29.57 m

• not sure

Poll

How do you feel about finding perimeter of these types of figures?

• Really Good!

• Good!

• Just ok!

• Not so good...