# 9-1 Practice Circles and Circumference

Circles are round shapes that can be found in everyday objects like wheels, clocks and coins. The circumferences of circles are an important element in geometry, as well as in everyday life. Understanding how to calculate circumference is a key skill for students to understand.

## What Is a Circle? A circle is a two-dimensional object with no sides or corners. All circles are made up of points equidistant from the center, known as the radius. The length of the radius is the same for all points. The circumference is the length of the path around the edge of a circle.

## How to Calculate the Circumference of a Circle The circumference of a circle can be calculated using the formula: circumference = 2πr. This equation requires the knowledge of the radius of the circle. The radius is the distance from the center of a circle to any point on its edge. To calculate the circumference, multiply the radius by 2 and then multiply that number by π. π is a constant with a value of 3.14.

## Example of Calculating the Circumference Let’s say a circle has a radius of 6 cm. To calculate the circumference, multiply the radius (6 cm) by two, which gives you 12 cm. Then, multiply that number by π (3.14) to get a circumference of 37.68 cm. Therefore, the circumference of the circle with a radius of 6 cm is 37.68 cm.

## The Importance of Knowing How to Calculate Circumference The ability to calculate circumference is an important skill for students to understand. By understanding this concept, students can better understand the properties of circles and how they are used in everyday life. Knowing how to calculate the circumference of a circle can also help students solve problems in other areas of mathematics, such as geometry and trigonometry.

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Circles and their circumferences are an important part of geometry and everyday life. Understanding how to calculate the circumference of a circle is a key skill for students to understand. Using the formula circumference = 2πr, students can easily calculate the circumference of a circle. Knowing how to calculate the circumference of a circle can help students solve problems in other areas of mathematics and understand the properties of circles in everyday life.