Area/Circumference of a Circle

• math

00:13

Value of Pi

For the purposes of this lesson, we can use either 3.14 or 22/7 for the value of Pi.

If you have a scientific calculator, the π sign will also get you Pi!

01:00

Formula for Diameter

d = r x 2

01:00

Try it!
If the diameter of the circle was 8 cm, what is the circumference?

1. 11.14 cm
2. 4.86 cm
3. 25.12
4. 2.54777 cm

01:20

Quick review on exponents!
"r squared" or "r raised to the second power" is the same as...

1. r x r
2. r x 2
3. r + r
4. r x r x r

02:29

Try it!
If the radius of the circle was 4 cm, what is the area?

1. 11.14 cm squared
2. 12.56 cm squared
3. 35.16 cm squared
4. 50.24 cm squared

05:46

What's the circumference of the Earth? Choose the closest answer.

1. 4,060.51 km
2. 40,035 km
3. 12,753.14 km
4. 80,070 km

06:35

What's the pizza's area?
Remember, to get the radius, you must divide the diameter in half!

1. 452.16 square inches
2. 45.859 square inches
3. 37.68 square inches
4. 147.14 square inches