Envision Math 2.0: Grade 7, Volume 2
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Envision Math 2.0: Grade 7, Volume 2 View details
6. Solve Problems Involving Area of a Circle
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Exercise 13 Page 453

Use the formula for finding the circumference of a circle.

28in.^2

Practice makes perfect

We want to find the area of a circular plate with circumference of 16.3 inches.

Remember that the area of a circle with radius r is calculated using the formula below. A=π r^2 Here, r is the radius of the circle. To find the area, we need to start by finding the value of the radius of the circle. Since the circumference is 16.3in., we can use the formula for the circumference to find the radius of the circle. C=2π r We will substitute 16.3 for C in the formula and solve the resulting equation for r. We will use 3.14 for π.
C=2 π r
16.3=2π r
16.3/2π=2π r/2π
16.3/2π=2π r/2π
16.3/2π=r
2.595554 ... =r
3 ≈ r
We found that the radius of the circular plate is approximately 3 inches. Now, we can substitute r= 3 into the formula for the area of a circle.
A=π r^2
A=π * 3^2
A=π * 9
A=28.26
A ≈ 28
The area of the circle is approximately 28in.^2.

Extra

More About Circles!

Are you interested in learning more about circles? Our Mathleaks original content can teach you all about them! Check out the following resources to see real-world uses for circumference and area, how circles compare to other shapes and why, as well as some higher level topics that you can look forward to learning about in Geometry and Algebra 2.