# Radius in Geometry: What is it and How to Calculate It

Radius is a term used in geometry to refer to the distance between the center of a circle and any point on its circumference. It is one of the most basic concepts in geometry and is a term used in many mathematical operations. Understanding radius can help to calculate the circumference, diameter, arc length, and area of a circle.

## What is Radius?

The radius is the line segment extending from the circle's center point to any point on its circumference. The radius is half the length of the diameter, which is the line segment connecting any two points on the circle that passes through the center. The radius can be used to calculate the circumference, arc length and area of a circle.

Circumference is the perimeter of a circle, and it can be calculated using the formula C=2pr, where r is the radius of the circle. The circumference can be thought of as the distance around a circle. The arc length of a circle is the length of a portion of the circumference, and it can be calculated using the formula s=?r, where ? is the measure of the central angle in radians and r is the radius of the circle.

The area of a circle can be calculated using the formula A=pr², where r is the radius of the circle. The area of a circle can be thought of as the total space inside the circle.

## How to Calculate Radius

The radius of a circle can be calculated using the formula r=d/2, where d is the diameter of the circle. The diameter can be calculated using the formula d=2r, where r is the radius of the circle. The circumference and arc length of a circle can also be used to calculate the radius, using the formula r=s/? or r=C/2p, respectively.

## Practice Problems

- Calculate the circumference of a circle with a radius of 6 cm.
- Answer: Circumference = 2pr = 2p(6 cm) = 12p cm

- Calculate the arc length of a circle with a radius of 4 cm and a central angle of 120°.
- Answer: Arc Length = ?r = (120°)(4 cm) = 480° cm

- Calculate the area of a circle with a radius of 5 cm.
- Answer: Area = pr
^{2}= p(5 cm)^{2}= 25p cm^{2}

- Answer: Area = pr
- Calculate the radius of a circle with a circumference of 10p cm.
- Answer: Radius = C/2p = (10p cm)/2p = 5 cm

- Calculate the radius of a circle with an arc length of 80° cm and a central angle of 90°.
- Answer: Radius = s/? = (80° cm)/(90°) = 0.89 cm

## Summary

Radius is an important concept in geometry and is used to calculate the circumference, arc length and area of a circle. The radius is the line segment extending from the circle's center point to any point on its circumference, and it is half the length of the diameter. The radius of a circle can be calculated using the formula r=d/2, where d is the diameter of the circle. It can also be calculated using the circumference and arc length of a circle, using the formulas r=C/2p and r=s/?, respectively.

## FAQ

### What is the best definition for a radius?

A radius is a line segment that connects the center of a circle or sphere to a point on its circumference or surface.

### How do you write a radius in geometry?

A radius is typically written as a letter 'r' with a straight line over it (??).

### What is radius give example?

For example, in the circle shown below, the length of the radius is 4 (?? = 4).