11­3 Area of a circle.notebook
March 02, 2016
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11­3 Area of a circle.notebook
March 02, 2016
Topic 11­3 Area of a circle
A = πr2
A = π r r
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11­3 Area of a circle.notebook
March 02, 2016
How are the areas of a circle and a parallelogram related?
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11­3 Area of a circle.notebook
March 02, 2016
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11­3 Area of a circle.notebook
March 02, 2016
Find the area of a circle in terms of π
1. The diameter is 20 ft.
2. The radius is 20 ft.
3. The diameter is 2 in.
4. The radius is 2 in.
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11­3 Area of a circle.notebook
March 02, 2016
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11­3 Area of a circle.notebook
March 02, 2016
Find the area of a circle. Use 3.14 for π.
1. The diameter is 20 ft.
2. The radius is 20 ft.
3. The diameter is 2 in.
4. The radius is 2 in.
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11­3 Area of a circle.notebook
March 02, 2016
How many times greater is the area of Circle 1 than the area of Circle 2?
The diameter of Circle X is 10 cm. The diameter of Circle Y is 25 cm. Which circle has the greater area and by how​ much? Use 3.14 for π. 8
11­3 Area of a circle.notebook
March 02, 2016
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11­3 Area of a circle.notebook
March 02, 2016
What do you do when the area of a circle is given to find the radius?
Example: The area of a circle is 36π cm2. What is the radius?
A = πr2
Step 1: Write out the formula.
Step 2: Substitute in what you know.
36π = πr2
Step 3: Isolate the r2 by dividing π on both sides
36π = πr2
π
π
36 = r2
Step 4: Square root (√ ) both sides
36
√ r2
=√ 6 =r
What do you do when the area of a circle is given to find the radius?
Example: The area of a circle is 113.04 cm2. What is the radius?
Use 3.14 for π.
A = πr2
Step 1: Write out the formula.
Step 2: Substitute in what you know.
113.04 = 3.14r2
Step 3: Isolate the r2 by dividing 3.14 on both sides
113.04 = 3.14r2
3.14 3.14
36 = r2
Step 4: Square root (√ ) both sides
36
√ r2
=√ 6 =r
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