Area of a circle

In this article, we will learn everything necessary about the area of a circle. First, we will know the formula to calculate the area of the circle and then, we will continue with questions on the topic that could appear in an exam and that you should know how to solve.
Shall we start?

The area of the circle represents "the interior" of the circumference. By finding the area, we actually obtain the surface "enclosed" within the circumference.

The part painted in orange is the area of the circle.

To calculate the area of the circle we must use the following formula:

$A = π \times R^2$

$A$ -> area of the circle
$\pi–>PI=3.14$
$R$ -> Radius of the circumference

Note - Notice that in the formula $R$ is raised to the second power. Those who are not comfortable operating with powers can replace $R^2$ with $R\times R$.

After understanding what each part of the formula implies, we can write it down like this:

Now let's move on to practice with some questions about the area of the circle.

Questions about the area of the circle when the radius is given

These are the easiest questions about the area of the circle since they require nothing more than placing the data in the formula.
The radius is already given and all you have to do is place it in the formula.

Let's practice:
Calculate the area of the circle knowing that the radius is $4$ cm.

Solution:
The given radius is $4$ cm.
We will place it in the formula to find the area of the circle and we will obtain:

$A=3.14\times4^2$
$A=3.14\times16$
$A=50.24$

Answer:
The area of the circle is $50.24$ $cm^2$ .

Given the circle

represents the center of the circumference.
What is the area of the circle?

Solution:

Observe: we know that $M$ represents the center of the circumference. Therefore, we deduce that the segment coming from there is the radius.
In the illustration, it is shown that the segment coming from $M$ measures $3$ cm.
That is, the radius measures $3$ cm.
We will place it in the formula and obtain:

$A=3.14\times3^2$
$A=3.14\times9$
$A=28.26$

Answer:
The area of the circle is $A=28.26$ $cm^2$.

More practice:

The radius measures $5$ cm.
What is the area of the circle?

Solution

The area of the circle can be calculated by placing the provided data:

$A=\pi\times R\times R=3.14\times5\times5=78.5$

Answer:

That is, the area of the circle is $78.5$ $cm^2$.

In this type of questions, we must carry out a preliminary step before placing the data in the formula.
The diameter of the circle is the chord that passes exactly through the center and is equal to two radii.
That is, to go from the diameter to the radius we must divide by $2$

Mode of action:
First step - Divide the diameter by $2$.
Second step - Place in the formula.

Let's practice:
Given a circle whose diameter measures $10$ cm.
What is the area of the circle?

Solution:
We realize that we were given the diameter, but we need the radius to place it in the formula. Therefore, we will divide the diameter by $2$ and arrive at the radius.

We will obtain :
$10:2=5$

The radius measures $5$ cm.
We will place it in the formula and obtain :

$A=3.14\times5^2$
$A=3.14\times25$
$A=78.5$

Answer:
The area of the circle is $78.5$ $cm^2$.

Observe the illustration and calculate the area of the circle.
\( M \ represents the center of the circumference.

\( ab=8 \ cm.

Solution:
We know that M represents the center of the circumference, therefore, the chord ab shown in the illustration is the diameter of the circle.
We will divide it by $2$ and arrive at the radius.
We obtain:
$8:2=4$

The radius measures $4$ cm. We will place it in the formula for the area of the circle and obtain:

$A=3.14\times4^2$
$A=3.14\times16$
$A=50.24$

Answer:
The area of the circle is $50.24$ $cm^2$.

In this type of problems, we will place the given area within the formula for calculating the area of the circle and, in this way, we will find the radius.
Remember $A$: represents the area of the circle.

Exercise:
The area of the circle is $153.86$
Calculate the radius of the circle.

Solution:
We will place in the formula:
$r^2\times3.14=153.86$
We divide by $3.14$
$49=r^2$
We will clear the root
$r=7$

Answer:

The radius measures $7$ cm.

If you are interested in learning how to calculate areas of other geometric shapes, you can enter one of the following articles:

• How is the area of a trapezoid calculated?
• How to calculate the area of a triangle
• The area of the parallelogram: what is it and how is it calculated?
• Surface area of triangular prisms
• How is the area of a rhombus calculated?
• How to calculate the area of a regular hexagon?
• Area of the rectangle
• How to calculate the area of an orthohedron
• Arcs in a circle

In the blog of Tutorela you will find a variety of articles about mathematics

Explanations in a more visual way.