Lesson 86

Circumference and Area of a Circle

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Learning Objectives

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

• identify the radius and diameter of a circle (Review)

What is Circumference?

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?

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

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

$$\pi r^2$$

• 12.56 sq units

• 25.12 sq units

• 50.24 sq units

• 200.96 sq units

Open Ended

Find the area of this circle.

$$\pi r^2$$

Open Ended

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