7.9B - Circumference and area of circles

7.9B - Circumference and area of circles

Draw

Students complete the STAAR ITEM BELOW. WHEN YOU FINISH REWORK THE PROBLEM WITH THE TEACHER IN THE VIDEO

Reorder

Reorder the following steps when solving for the area of a circle

• Write the equation from the formula chart

• Substitute the given values from the problems, for the variables in the formula

• Perform the multiplication

• Perform, division (if necessary only if given the area)

• Calculate the final answer (rounding if necessary)

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• 2
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• 5

What is Circumference?

Multiple Choice

True or False: The diameter is being pictured here.

• True

• False

How do I find the circumference using the formula?

Example 1: The diameter of a circle is 12 cm. What is the circumference?

Example 2: The radius of a circle is 5 inches. What is the circumference?

Multiple Choice

Find the circumference. Leave your answer in terms of pi. 

 

• 8 $$\pi$$  

• 4

• 2 $$\pi$$  

• 4 $$\pi$$  

Example 1: Find the area of a circle if the radius is 8 cm. Leave your answer in terms of pi. 

Example 2: Find the area of a circle if the diameter is 12 inches. Use 3.14 for pi. 

Multiple Choice

Find the area of this circle. Leave your answers in terms of pi. 

• $$25\pi$$

• $$5\pi$$

• $$10\pi$$

• $$100\pi$$

Open Ended

Find the area of a circle if the radius is 7 inches. Use 3.14 for pi.

Circumference and Area of a Circle

Dropdown

The diameter of the smaller circle is ​

Select answer

. The diameter of the medium circle is ​

Select answer

. The diameter of the larger circle is ​

Select answer

. However, in order to find the area of any circle you will need the ​

Select answer

​ which is ​

Select answer

of the diameter.

Learning Objectives

• Today, we will determine how to find the circumference and area of a circle

• identify the radius and diameter of a circle

Match

Using the picture, match the correct area equations

• $$A\ =\ \pi r^2$$

• $$A\ =\ \pi r^2$$

  $$A\ =\ \pi3^2$$

  $$A\ =\ 9\pi$$

• $$A\ =\ \pi r^2$$

  $$A=\pi6^2$$

  $$A=36\pi$$

• $$A\ =\ \pi r^2$$

  $$A\ =\ \pi9^2$$

  $$A\ =\ 81\pi$$

Area formula

Area of the smaller circle

Area of the medium circle

Area of the larger circle

• Area formula

• Area of the smaller circle

• Area of the medium circle

• Area of the larger circle

What is Circumference?

Drag and Drop

The radius of the railroad-crossing sign is ​

Placeholder

. Using $$\pi\approx3.14$$ The circumference of the sign is ​ ​

Placeholder

The area of the sign is ​

Placeholder

Drag these tiles and drop them in the correct blank above

15 in

94.2 in

30 in

Multiple Choice

True or False: The diameter is being pictured here.

• True

• False

Multiple Choice

True or False: The diameter is twice as long as the radius.

• True

• False

Multiple Choice

The diameter of a circle is 10 inches. What is the radius?

• 10 inces

• 20 inches

• 5 inches

• 2.5 inches

Open Ended

The radius of a circle is 12 cm. What is the diameter?

How do I find the circumference using the formula?

Example 1: The diameter of a circle is 12 cm. What is the circumference?

Example 2: The radius of a circle is 5 inches. What is the circumference?

Multiple Choice

Find the circumference. Leave your answer in terms of pi. 

 

• 8 $$\pi$$  

• 4

• 2 $$\pi$$  

• 4 $$\pi$$  

Open Ended

Find the circumference of a circle if the radius is 2.5 inches. Use 3.14 for pi.

Area of a Circle

Example 1: Find the area of a circle if the radius is 8 cm. Leave your answer in terms of pi. 

Example 2: Find the area of a circle if the diameter is 12 inches. Use 3.14 for pi. 

Multiple Choice

Find the area of this circle. Leave your answers in terms of pi. 

• $$25\pi$$

  
  

• $$5\pi$$

• $$10\pi$$

• $$100\pi$$

Multiple Choice

What is the area of this circle? Use 3.14 for pi. 

• 12.56

• 25.12

• 50.24 

• 200.96

Open Ended

Find the area of a circle if the radius is 7 inches. Use 3.14 for pi.