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Area & Circumference of Circles
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What you will learn from this videoWhat you will learn
- We’ll learn how to calculate the circumference of a circle.
- We will also learn how to find the area of a circle given its diameter.
- And we will see how this knowledge can help us play a game of frisbee, decorate for a party and even buy a swimming pool.
- Discussion Questions
Before Video
What is perimeter? What units can you use to describe perimeter?ANSWERPerimeter is the distance around a 2D shape. You can use units like meters, centimeters, or inches.
Area is the amount of space inside a 2D shape. You can use units like square meters, square centimeters, or square inches.
Its perimeter is 28 cm. Its area is 40 cm^{2}.
Divide both sides by w.
The square of a number is the number multiplied by itself. For example, 9^{2} = 9 x 9 = 81.
After Video
What is the radius of a circle? What is the diameter of a circle? How are they related?ANSWERThe radius is a line from the center of a circle to the edge. The diameter is a line from one side of a circle to the other that passes through the center. The diameter is twice as long as the radius.
Pi is a special number. It is the ratio of the circumference of a circle to its diameter. It is an irrational number, so its decimal form never ends or repeats. It is approximately 3.14.
The circumference is the perimeter of a circle, or the distance around the outside of the circle. C = πd or C = 2πr
A = πr^{2}
36π cm^{2}, or approximately 113.04 cm^{2}
- Vocabulary
- Perimeter DEFINE
The distance around a 2D shape.
- Area DEFINE
The amount of space inside a 2D shape.
- Circumference DEFINE
The distance around a circle.
- Diameter DEFINE
The distance straight across a circle. The diameter always passes through the center point of the circle.
- Pi (π) DEFINE
The ratio of the circumference of a circle to its diameter. This is always the same number: approximately 3.14. The actual number is an irrational number.
- Radius DEFINE
The measurement from the center of a circle to its edge. The radius is half the diameter.
- Irrational number DEFINE
A decimal that never ends or repeats. Pi is an irrational number.
- Perimeter DEFINE
- Reading Material
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide