Circumference of a Circle

Circumference of a Circle

Based on Lesson by Courtney Tout

Warm-Up
Let's see what you remember!

Multiple Choice

Diameter 32 inches
What is the radius?

• 16 inches
• 64 inches
• 96 inches
  96 inches
• 16 ft 

Multiple Choice

If my radius is 10ft, what is my diameter?

• 20ft
• 5ft
• 31.4ft
• 62.8ft

Multiple Choice

What does "circumference" mean?

• Space a circle takes up
• Distance around a circle
• Line from one side of a circle to another
• Line from center of circle to side

Multiple Choice

What is the measurement around the outside of a circle called?

• Diameter

• Circumference

• Radius

• Center

We will use the formula:

​

​

When we are given diameter.​

​

​​Formulas for Circumference​

We will use the formula:

​

​

When we are given radius.​

Multiple Choice

What is the formula for finding the circumstance of a circle with just the diameter?

•  π*d
• b*h
• l*w*h
• I do not know

Multiple Choice

Other than the formula C=πd what is another formula for circumference of a circle?

• C=2π
• C=2πr
• C=πr²
• C=πd²

Multiple Choice

Choose the answer which best describes how these formulas are related to each other.

• They both solve for circumference. In the first formula it uses diameter, in the second formula it uses two times the radius, which is the same thing as diameter.

• They both solve for circumference, in the first uses diameter and the second uses pi.

• They both solve for area. In the first formula it uses diameter, in the second formula it uses two times the radius, which is the same thing as diameter.

• They both use circumference to solve for pi. One uses radius, the other uses diameter.

​C = d x Pi

Pi = π

​

Set it Up:

C = 6.2 x ​π
(We use the π button on the calculator)

​Given Diameter​

Given Radius​

​

​Set It Up

Multiple Choice

Which Formula would you use?

Multiple Select

What are ALL the ways we can set this problem up?

• $$C\ =\ 2\ \times17\times3.14$$  

• $$C=2\times17\times\pi$$  

• $$C=17\times3.14$$  

• $$C=17\pi$$  

Multiple Choice

Which Formula would you use?

Multiple Select

What are ALL the ways we can set this up?

• $$C=15.8\pi$$  

• $$C=2\times15.8\times\pi$$  

• $$C=15.8\times3.14$$  

• $$C=2\times15.8\times3.14$$  

• ​Select correct formula

​ C = dΠ​

Solving for Circumference​​

• Fill-In Information

​ C = 8 x Π​

C = 8 x 3.14​

• Multiply to solve:

​ C = ​25.12 m

3.14

x 8​

25.12​

• ​Select correct formula

​ C = 2 x r x Π​

Solving for Circumference​​

• Fill-In Information

​ C = 2 x 7.2 x Π​

C = 14.4 x 3.14

• Multiply to solve:

​ C = ​45.216 m

14.4

x3.14​

576

1440

+43200

45.216​

Multiple Choice

Find the circumference of the circle. Round to the nearest tenth

• 78.5

• 15.7 ft

• 62.8 ft

• 31.4 ft

Multiple Choice

Find the circumference of the circle. Round to the nearest tenth.

• 125.6 km

• 31.4 km

• 62.8 km

• 15.7 km

Multiple Choice

Find the circumference (to the nearest whole number)

• 88 in
• 44 in
• 116 square in
• None of the above

Multiple Choice

Find the circumference of the circle. Round to the nearest tenth.

• 18.84 cm

• 9.42 cm

• 37.68 cm

• 4.71 cm

Open Ended

After going through this lesson, which type of problem(s) do you feel like you can do well? Explain.

Open Ended

After going through this lesson, which type of problem(s) do you feel like you are still struggling with? Explain.