Circumference of a Circle

Circumference of a Circle

By Courtney Tout

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Warm-Up

​Some text here about the topic of discussion.

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 or C = 6.2 x 3.14

​Given Diameter​

Given Radius​

​

​C = 2 x r x pi

pi = Π

​

Set it Up:

​

C = 2 x 14 x ​Π or C = 2 x 14 x 3.14

​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.

• 78.5

• 15.7 ft

• 62.8 ft

• 31.4 ft

Multiple Choice

Find the circumference of the circle.

• 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.

• 18.84 cm

• 9.42 cm

• 37.68 cm

• 4.71 cm

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