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Warm Up. Problem of the Day. Lesson Presentation. Lesson Quizzes. Warm Up Simplify. 1. 8 2 2. 12 2 3. 6.2 2 4. 7.5 2. 64. 144. 38.44. 56.25. Problem of the Day A 16 in. pizza sells for $11.99. A 10 in. pizza sells for $5.99. Which size gives you more pizza per penny? Explain.

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Warm Up

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Warm up

Warm Up

Problem of the Day

Lesson Presentation

Lesson Quizzes


Warm up

Warm Up

Simplify.

1. 82

2. 122

3. 6.22

4. 7.52

64

144

38.44

56.25


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Problem of the Day

A 16 in. pizza sells for $11.99. A 10 in. pizza sells for $5.99. Which size gives you more pizza per penny? Explain.

The larger pizza; you get more than twice as much (64 in2 instead of 25in2) for about twice the price.


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Sunshine State Standards

Prep for MA.7.G.2.1 Justify and use formulas for surface area and volume of pyramids, prisms, cylinders, and cones.

Review of MA.6.G.4.1


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A circle can be cut into equal-sized sectors and arranged to resemble a parallelogram. The height h of the parallelogram is equal to the radius r of the circle, and the base b of the parallelogram is equal to one-half the circumference C of the circle.

So the area of the parallelogram can be written as

1

2

Cr.

A = bh, or A =

1

2

Since C = 2r, A =

(2r)r = r2.


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Remember!

The order of operations calls for evaluating the exponents before multiplying.

Additional Example 1A: Finding the Area of a Circle

Find the area of the circle to the nearest tenth. Use 3.14 for .

A = r2

Use the formula.

7 cm

A 3.14 · 72

Substitute 7 for r.

A 3.14 · 49

Evaluate the power.

Multiply.

A  153.86

The area of the circle is about 153.9 cm2.


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Additional Example 1B: Finding the Area of a Circle

Find the area of the circle to the nearest tenth. Use 3.14 for .

A = r2

Use the formula.

A 3.14 · 92

Substitute 9 for r.

18 ft

A 3.14 · 81

Evaluate the power.

Multiply.

A  254.34

The area of the circle is about 254.3 ft2.


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Check It Out: Example 1A

Find the area of the circle to the nearest tenth. Use 3.14 for .

A = r2

Use the formula.

A 3.14 · 102

10 cm

Substitute 10 for r.

A 3.14 · 100

Evaluate the power.

Multiply.

A  314

The area of the circle is about 314 cm2.


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Check It Out: Example 1B

Find the area of the circle to the nearest tenth. Use 3.14 for .

A = r2

Use the formula.

12 ft

A 3.14 · 62

Substitute 6 for r.

A 3.14 · 36

Evaluate the power.

Multiply.

A  113.04

The area of the circle is about 113.0 ft2.


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Additional Example 2: Application

Park employees are fitting a top over a circular drain in the park. If the radius of the drain is 14 inches, what is the area of the top that will cover the drain? Use

22

7

for .

A =  r2

Use the formula for the area of a circle.

22

7

·142

Substitute. Use 14 for r.

A 

28

22

7

196

·

A 

Evaluate the power.

1

A 22 · 28

Multiply.

A 616

The area of the top that will cover the drain is about 616 in2.


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Check It Out: Example 2

Albert was designing a cover for a spa. If the radius of the spa is 7 ft, what is the area of the cover that will be made? Use

22

7

for .

A =  r2

Use the formula for the area of a circle.

22

7

·72

A 

Substitute. Use 7 for r.

7

22

7

49

·

A 

Evaluate the power.

1

A 22 · 7

Multiply.

A 154

The area of the top that will cover spa is about 154 ft2.


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Additional Example 3: Application

Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.

1.5 cm

The measurement of the radius of the circle is 1.5 cm.

Now find the area of the entire circle.

A = r2

Use the formula for the area of a circle.

Substitute. Use 1.5 for r.

A = 3.14 · 1.52

A  3.14 · 2.25

Evaluate the power.

Multiply.

A 7.07


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1 2

Since of the circle is shaded, divide the area of the

circle by 2. 7.07 ÷ 2 = 3.535.

Additional Example 3 Continued

Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.

The area of the shaded region of the circle is about 3.5 cm2.


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Check It Out: Example 3

Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.

2.4 cm

The measurement of the radius of the circle is 2.4 cm.

Now find the area of the entire circle.

A = r2

Use the formula for the area of a circle.

Substitute. Use 2.4 for r.

A = 3.14 · 2.42

A  3.14 · 5.76

Evaluate the power.

Multiply.

A 18.09


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3 4

Since of the circle is shaded, divide the area of the

circle by 4 and subtract the answer from the entire area. 18.0864 ÷ 4 = 4.52. 18.0864 – 4.52 = 13.56.

Check It Out: Example 3 Continued

Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.

The area of the shaded region of the circle is about 13.56 cm2.


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Lesson Quizzes

Standard Lesson Quiz

Lesson Quiz for Student Response Systems


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Lesson Quiz

Find the area of each circle, to the nearest tenth. Use 3.14 for .

1.

3. The bull’s-eye on a target has a diameter of 2 in.What is the area of the bull’s-eye to the nearest tenth? Use 3.14 for .

4. A round tablecloth has a radius of 36 in. What isthe area of the tablecloth? Use 3.14 for . Roundyour answer to the nearest tenth.

8 ft

2.

9 ft

201.0 ft2

63.6 ft2

3.1 in2

4,069.4 in2


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Lesson Quiz for Student Response Systems

1. Identify the area of the circle to the nearest tenth. Use 3.14 for .

A. 907.5 ft2

B. 289 ft2

C. 226.9 ft2

D. 53.4 ft2

17 ft


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Lesson Quiz for Student Response Systems

2. Identify the area of the circle to the nearest tenth. Use 3.14 for .

A. 72.2 in2

B. 144.4 in2

C. 415.3 in2

D. 1661.1 in2

23 in.


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Lesson Quiz for Student Response Systems

3. A round table has a diameter of 11 ft. What is the area of the table to the nearest tenth? Use 3.14 for .

A. 95 ft2

B. 69.1 ft2

C. 54.2 ft2

D. 34 ft2


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