Finding the Radius of a Circle: Formula and Examples

In this publication, we will look at how you can calculate the radius of a circle (circle) and analyze examples of solving problems to fix the material.

Formulas for calculating the radius of a circle

1. Through the circumference / perimeter of the circle

The radius of a circle/circle is calculated by the formula:

C is the circumference/perimeter of the circle; equals twice the product of the number π to its radius:

C = 2πR

π – a number whose approximate value is 3,14.

2. Through the area of the circle

The radius of the circle/circle is calculated in this way:

S is the area of ​​the circle; is equal to the number πtimes the square of its radius:

S = πR²

Examples of tasks

Task 1

The circumference is 87,92 cm. Find its radius.

Decision:

We use the first formula (through the perimeter):

Task 2

Find the radius of the circle if its area is 254,34 см².

Decision:

We will use the formula expressed through the area of the figure: