Transcript Area of Circles

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
The area of a circle equals
the product of pi () and
the square of its radius.
Area = r²
r
Find the Area of the Circle
Round the answer to the nearest tenth.
4 cm
•Area = r²
•A = (4²)
•A = (16)
•A = 50.3 cm²
Find the Area of the Circle
Round the answer to the nearest tenth.
•Area = r²
8 in
•A = (8²)
•A = (64)
•A = 201.1 in²
Find the Area of the Circle
Round the answer to the nearest tenth.
•Area = r²
11 ft
1. Use the diameter
to find the radius.
2. 11 ÷ 2 = 5.5
3. Radius = 5.5 ft
•A = (5.5²)
•A = (30.25)
•A = 95.0 ft²
Find the Area of the Circle
Round the answer to the nearest tenth.
•Area = r²
6.5 m
1. Use the diameter
to find the radius.
2. 6.5 ÷ 2 = 3.25
3. Radius = 3.25 m
•A = (3.25²)
•A = (10.5625)
•A = 33.2 m²
Find the area to the nearest tenth.
25.6 m
9.8 in
•Area = r²
•Area = r²
•A = (12.8²)
•A = (9.8²)
•A = (163.84)
•A = (96.04)
•A = 514.7 m²
•A = 301.7 in²
Area of a Semi-Circle
•Area = r²
•A = (13²)
26 ft
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
•A = (169)
•A = 530.9 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)