Prime Time

• Circle the seven prime numbers that, when added together, equal 75.

• 3, 11, 14, 13, 5, 17, 12, 6, 19, 23, 7, 9

• Remember a prime number is a number that has only two factors, 1 and itself.

• 2 is prime : 1x2

Prime Time Solution

• 3 + 5 + 7 + 11 + 13 + 17 + 19 = 75

Area of Circles

Lesson 11-6

Review of Circles

r d

The radius of a circle is half of the diameter. Divide the diameter by 2 to get the radius.

Area of a Circle

r

The area of a circle equals the product of pi () and the square of its radius.

Area = r²

Find the Area of the CircleRound the answer to the nearest tenth.

4 cm •Area = r²

•A = (4²)

•A = (16)

•A = 50.3 cm²

Find the Area of the CircleRound the answer to the nearest tenth.

8 in

•Area = r²

•A = (8²)

•A = (64)

•A = 201.1 in²

Find the Area of the CircleRound the answer to the nearest tenth.

11 ft

•Area = r²

•A = (5.5²)

•A = (30.25)

•A = 95.0 ft²

1. Use the diameter to find the radius.

2. 11 ÷ 2 = 5.5

3. Radius = 5.5 ft

Find the Area of the CircleRound the answer to the nearest tenth.

6.5 m

•Area = r²

•A = (3.25²)

•A = (10.5625)

•A = 33.2 m²

1. Use the diameter to find the radius.

2. 6.5 ÷ 2 = 3.25

3. Radius = 3.25 m

Find the area to the nearest tenth.

25.6 m

•Area = r²

•A = (12.8²)

•A = (163.84)

•A = 514.7 m²

9.8 in

•Area = r²

•A = (9.8²)

•A = (96.04)

•A = 301.7 in²

Area of a Semi-Circle

26 ft

•Area = r²

•A = (13²)

•A = (169)

•A = 530.9 ft² 1. 530.9 ft² is the area of the whole circle. How can you find the area of half the circle.

2. Divide the area by 2. A semi- circle is half of a circle.

3. Answer: 265.5 ft²

Homework

• Lesson 11-6 # 2-16 even

• TEST: On Friday, lesson 11-5 (area of triangles and trapezoids), lesson 11-6 (area of circles), and lesson 11-7 (we will complete this tomorrow)