How do you find the area of a circle?
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Transcript of How do you find the area of a circle?
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How do you find the area of a circle?
For Example
A circle has a diameter of 10 meters. What is the area of the circle?
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In this lesson you will learn to find the area of a circle by exploring the relationship
between a circle and a rectangle.
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Let’s ReviewLet’s Review
Area of Rectangle = l x w
A = 5cm x 9cm
5 cm
9 cm
A = 45 cm2
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Let’s ReviewLet’s Review
Multiplying a number or variable by itself is known as squaring it.
9 x 9 = 92 = 81
r x r = r2
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Let’s ReviewA Common Mistake
Remember the Order of Operations. Exponents come before multiplication.
A = (3.14)(4)2
A = (12.56) 2
Wrong
A = 157.7536
Correct
A = (3.14)(16)A = 50.24
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Let’s ReviewCore Lesson
A pizza has a radius of 9 inches. What is the area of the pizza?
r = 9 inches
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Let’s ReviewCore Lesson
Area of a Circle =πr2
πr
r
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Let’s ReviewCore Lesson
A = π(9in.)2
A = 3.14(81in.2)
A = 254.34in.2
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Let’s ReviewCore Lesson
Find the area of a circle with a diameter of 10 meters. Do not approximate pi.
A = π(5m)2
A = 25πm2
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In this lesson you have learned to find the area of a circle by
exploring the relationship between circles and
rectangles.
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Let’s ReviewGuided Practice
What is the area of a circle that has a radius of 6 cm? Use 3.14 for pi.
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Let’s ReviewExtension Activities
Susan drew a circle with a radius of 4 inches and Ellen drew a circle with a radius of 8 inches. Ellen said “since the radius of my circle with twice the radius of your circle, the area of my circle is twice the area of your circle.” Is Ellen’s statement correct? If not, explain what Ellen could say instead.
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Let’s ReviewExtension Activities
A circle is inside of a square, as shown below. The edges of the square each touch a point on the circle. If the square has an area of 16 square meters, what is the area of the circle?
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Let’s ReviewExtension Activities
A circular pizza can feed 4 people if it has an area of at least 200 square inches. A pizza
from Joe’s Pizza has a radius of 9 inches. Is it enough to feed a family of 4?