How To Find Radius of a Circle

calculate radius of a circle

This article will show you how to find the radius of a circle but at first lets see definition of a circle. Many mathematicians must be familiar with a circle.

The circle is one kind of geometry in mathematics. It has a very special shape among other geometry.

If geometry has angles, a circle doesn’t have it. So it will be more difficult to find its circumference and area. Thanks to scientists, they have found the way to find area and circumference of a circle.

So, how to find the radius of a circle? We will see it below.

Formula for Radius of a Circle

If you want to know how to find the area of a circle and its circumference, it is important to know that we have to find out circle radius and diameter.

Radius is an imaginary half straight line that stretched from each end of a circle, which diameter is a full straight line. Each radius and diameter are used in calculating circle area and circumference.

But the new question is come out, how we solve that problem?We are even don’t know the value.

Find Radius If Area is Known

how to find radius of a circle

Study it carefully, it will be easy to know how to find the radius of a circle without knowing its value. You must know the area of a circle formula to find its radius.

The formula of circle area using radius is A = πr2. Just divided A with phi. After that, square root the result. And you’ll find the radius. It is easy to solve using the area formula.

Example, you have area 12,56 cm2. Then divided with π, which has valued 3,14. The result is 4. Then square rooted it. The radius is 2 cm.

Find Radius If Circumference is Known


If you don’t know the area, don’t worry. We can find the radius using the circumference of a circle formula. The formula of circle circumference is C = 2πr. 

Just divided C with 2π , and the radius will directly be known. It is similar to the number one way, just using divided. But the difference in this way you don’t have to square root the results.

Example, you have circumference 12,56 cm. Then divided with 2 π (2 x 3,14 = 6,28). And you will find the radius is 2 cm.

After we know how to find the radius of a circle, we guess all of your tasks will be easier to solve the more problem that related with a circle, such as the volume of ball, cone or cylinder.

Drill yourself with all the way, so it will be helpful for you in the future.

Don’t forget to read our other articles to help your problem and give you additional information.

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