Circle Geometry Concepts and Formulas

This video tutorial teaches how to find the area of a circle using its circumference. It begins with a review of the formulas for area and circumference, highlighting a common mistake where students use the diameter instead of the radius in calculations. The tutorial then provides examples, including one with an exact pi value and another with an approximated pi value, to demonstrate the correct method of finding the area. By the end, viewers will understand how to correctly calculate the area of a circle using its circumference.

What is the formula for the area of a circle?

• pi times diameter squared

• pi times radius squared

• pi times diameter

• 2 times pi times radius

What is the formula for the circumference of a circle?

• pi times diameter squared

• pi times radius

• 2 times pi times radius

• pi times radius squared

What is a common mistake when calculating the area of a circle?

• Using diameter instead of radius

• Using radius instead of diameter

• Using pi as 3

• Using circumference as area

If a circle has a diameter of 6 cm, what is the correct area?

• 36 pi cm squared

• 9 pi cm squared

• 18 pi cm squared

• 12 pi cm squared

What is the diameter of a circle if its circumference is 18 pi yards?

• 36 yards

• 18 yards

• 9 yards

• 27 yards

What is the area of a circle with a radius of 9 yards?

• 18 pi yards squared

• 81 pi yards squared

• 36 pi yards squared

• 9 pi yards squared

If the circumference of a circle is approximately 37.68 cm, what is the diameter using pi as 3.14?

• 12 cm

• 9 cm

• 18 cm

• 6 cm

What is the radius of a circle with a diameter of 12 cm?

• 6 cm

• 3 cm

• 9 cm

• 12 cm

What is the approximate area of a circle with a radius of 6 cm using pi as 3.14?

• 18 cm squared

• 72 cm squared

• 36 cm squared

• 113.04 cm squared

What have you learned in this lesson?

• How to approximate pi

• How to calculate the radius from the area

• How to find the area of a circle using circumference

• How to find the diameter of a circle