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Glencoe Math: Course 2, Volume 2

GM

Glencoe Math: Course 2, Volume 2 View details

Mid-Chapter Check

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Exercise 5 Page 650

The circumference of a circle equals π times twice its radius. The area of a circle equals the product of π and the square of its radius.

Circumference: about 52.8 miles
Area: about 221.6mi^2

Practice makes perfect

Let's consider the given circle.

Circle

We want to find the circumference and area of the circle. Let's do these things one by one.

Finding the Circumference

Recall that the circumference C of a circle equals π times twice its radius r. C = 2 π r Since the diameter of the circle is 16.8 miles, the radius of the circle is ( 12* 16.8) miles or 8.4 miles. Let's calculate the circumference using this information. Remember, we are asked to use 3.14 as an estimation of π.

C = 2π r

r= 8.4

C = 2π (8.4)

π ≈ 3.14

C ≈ 2 (3.14) (8.4)

Multiply

C ≈ 52.752

Round to 1 decimal place(s)

C ≈ 52.8

We found that C ≈ 52.8, which means that the circumference of the circle is about 52.8 miles.

Finding the Area

Recall that the area A of a circle equals the product of π and the square of its radius r. A = π r^2 Let's calculate the area of the given circle. Again, we will substitute 8.4 for r and 3.14 for π.

A = π r^2

r= 8.4

A = π ( 8.4^2)

π ≈ 3.14

A ≈ 3.14 (8.4^2)

Calculate power

A ≈ 3.14 (70.56)

Multiply

A ≈ 221.5584

Round to 1 decimal place(s)

A ≈ 221.6

The area of the circle is about 221.6 square miles.

Subchapter links

Vocabulary Check p.650

Skills Check and Problem Solving p.650