Area and Circumference of Circles

In this video, Mr. Dell explains how to calculate the area and circumference of circles, and extends these concepts to composite figures. The video covers finding the area of a circle using the formula πr², and the circumference using πd or 2πr. It also demonstrates how to calculate the area and perimeter of composite figures, including shaded regions and figures combining rectangles and semi-circles. The video uses approximations for π and emphasizes understanding the calculations both with and without a calculator.

What is the main focus of this video tutorial?

• Exploring the area and circumference of circles and composite figures

• Understanding the properties of triangles

• Finding the area and perimeter of squares

• Learning about the volume of cubes

What is the formula for the area of a circle?

• πd

• πr²

• 2πd

• 2πr

If a circle has a radius of 3 cm, what is its area using π ≈ 3.14?

• 56.52 cm²

• 18.84 cm²

• 28.26 cm²

• 9.42 cm²

What is the formula for the circumference of a circle?

• πr²

• 2πr

• πd

• r²

If a circle has a radius of 3 cm, what is its circumference using π ≈ 3.14?

• 28.26 cm

• 56.52 cm

• 9.42 cm

• 18.84 cm

How do you find the radius if the diameter of a circle is given?

• Subtract 2 from the diameter

• Multiply the diameter by 2

• Divide the diameter by 2

• Square the diameter

What is the area of a circle with a diameter of 10 feet using π ≈ 3.14?

• 78.5 ft²

• 31.4 ft²

• 50 ft²

• 25 ft²

What is the circumference of a circle with a diameter of 10 feet using π ≈ 3.14?

• 25 ft

• 31.4 ft

• 78.5 ft

• 50 ft

How do you find the area of a shaded region that is one-third of a circle?

• Subtract the area of the circle from itself

• Multiply the area of the circle by 3

• Divide the area of the circle by 3

• Add the area of the circle to itself

What is the area of a shaded region that is one-third of a circle with a radius of 12 feet using π ≈ 3.14?

• 150.72 ft²

• 405.16 ft²

• 50.24 ft²

• 200.58 ft²