In this page we practice finding the area of a circle using the formula:
\(A=\pi r^2\)
We also practice using the radius and diameter to calculate the area
Example 1
Find the area of a circle with radius:
\(r=2 \text{ cm}\)
Using the formula:
\(A=\pi r^2\)
\(A=π(2)2=4π \text{ cm}^2\)
Using \(\pi \approx 3.14\):
\(A \approx 12.56 \text{ cm}^2\)
So, the area is:
\(4π \text{ cm}^2\) or approximately \(12.56 \text{ cm}^2\)
Example 2
Find the area of a circle with radius:
\(r=5 \text{ m}\)
\(A=π(5)^2 \)
\(A=25π \text{ m}^2\)
Using \(\pi \approx 3.14\):
\(A \approx 78.5 \text{ m}^2\)
So, the area is:
\(25 \pi \text{ m}^2\) or approximately \(78.5 \text{ m}^2\)
Example 3
A circle has diameter:
\(d=10 \text{ cm}\)
First find the radius:
\(r=\frac{d}{2} = \frac{10}{2} = 5 \text{ cm}\)
Now use the area formula:
\(A=π(5)^2=25π \text{ cm}^2\)
\(A \approx 78.5 \text{ cm}^2\)
So, the area is:
\(25 \pi \text{ cm}^2\) or approximately \(78.5 \text{ cm}^2\)
Key Idea
When a circle is divided into many slices and rearranged, it begins to look like a rectangle.
- Rectangle length → \(\pi r\)
- Rectangle width → \(r\)
So:
\(A=(\pi r)(r)=\pi r^2\)
Practice
- More Examples (Current page)
- Take the Quiz
Continue Learning
- What is \(\pi\) (pi)? An Easy Explanation
- Why the Area of a Circle is \(\pi r^2\) (Visual Explanation)