# Circles

Learn how how to find the Area and Circumference of Circles when you have the radius or the diameter of the circle.

## Step by step guide to solve Circles

• In a circle, variable $$r$$ is usually used for the radius and $$d$$ for diameter and $$π$$ is about $$3.14$$.
• Area of a circle $$=πr^2$$
• Circumference of a circle $$=2πr$$

### Example 1:

Find the area of the circle.

Solution:

Use area formula: Area $$=πr^2$$,
$$r=6$$ $$in$$, then: Area $$=π(6)^2=36π, π=3.14$$ then: Area $$=36×3.14=113.04$$ $$in^2$$

### Example 2:

Find the Circumference of the circle.

Solution:

Use Circumference formula: Circumference $$=2πr$$
$$r=9$$ $$cm$$ , then: Circumference $$=2π(9)=18π$$
$$π=3.14$$ then: Circumference $$=18×3.14=56.52$$ $$cm$$

### Example 3:

Find the area of the circle.

Solution:

Use area formula: Area $$=πr^2$$,
$$r=6$$ $$in$$, then: Area $$=π(4)^2=16π, π=3.14$$ then: Area $$=16×3.14=50.24$$ $$in^2$$

### Example 4:

Find the Circumference of the circle.

Solution:

Use Circumference formula: Circumference $$=2πr$$
$$r=9$$ $$cm$$ , then: Circumference $$=2π(6)=12π$$
$$π=3.14$$ then: Circumference $$=12×3.14=37.68$$ $$cm$$

## Exercises

### Find the area and circumference of each circle. $$(\pi=3.14)$$

1. $$\color{blue}{Area: \ 50.24 \ in^2 , \ Circumference: \ 25.12 \ in}$$
2. $$\color{blue}{Area: \ 1,017.36 \ cm^2, \ Circumference: \ 113.04 \ cm}$$
3. $$\color{blue}{Area: \ 78.5 \ m^2, \ Circumference: \ 31.4 \ m}$$
4. $$\color{blue}{Area: \ 379.94 \ cm^2 , \ Circumference: \ 69.08 \ cm}$$