## Perimeter of a Circle Lesson

### How to Find the Perimeter of a Circle

The perimeter of a circle is called the circumference. The formula for perimeter of a circle is the circumference formula. It is given as:

**C = 2πr**

or:

**C = πd**

Where *C* is the circumference, *r* is the radius of the circle, and *d* is the diameter of the circle.

Here is an example of using this formula to find circumference of a circle with a radius of 3:

**C = 2π(3) = 6π, circumference = 6π.**

### Perimeter of a Circle Example Problems

Let's go through a couple of example problems together to practice finding the perimeter of a circle.

#### Example Problem 1

Find the circumference of a circle with a radius of 10.

Solution:

- Let's plug the radius into the circumference formula.
- C = 2πr = 2π(10) = 20π
**The circumference is 20π.**

#### Example Problem 2

Find the circumference of a circle with a diameter of 10.

Solution:

- Let's plug the diameter into the circumference formula.
- C = πd = π(10) = 10π
**The perimeter is 10π.**

#### Example Problem 3

Compare the perimeter of a circle with a diameter of 7 to a square with a side length of 7. The formula for perimeter of a square is P = 4s.

Solution:

- Let's plug the circle's diameter into the circumference formula. Solving for circumference gives us the perimeter.
- C = πd = π(7) = 7π.
- Now let's do the same for the square.
- C = 4s = 4(7) = 28
**The circle's perimeter is 7π (≈22) and the square's perimeter is 28.**