Skill: Calculate the area of circles

To find the area of a circle, use the formula

$$A=\pi r^2$$

where $r$ is the radius. The radius is the distance from the center of the circle to its edge.

If you are given the diameter, divide it by $2$ to find the radius.

Example: Find the area of a circle with a diameter of $12\text{ cm}$.

1. Find the radius:

$$r=\frac{12}{2}=6\text{ cm}$$

2. Substitute the radius into the area formula:

$$A=\pi(6)^2$$

3. Square the radius:

$$A=36\pi\text{ cm}^2$$

This is the exact area. Using $\pi\approx 3.14$:

$$A\approx 36(3.14)=113.04\text{ cm}^2$$

The area is $\boxed{36\pi\text{ cm}^2}$, or approximately $\boxed{113.04\text{ cm}^2}$.