Chord of a Circle – Formula, Definition With Examples
Updated on January 14, 2024
Welcome to another exciting journey with Brighterly, where we explore the fascinating world of geometry. Today, we are delving into the concept of the “Chord of a Circle.” If you’ve ever looked at a pizza slice or the spokes of a bicycle wheel, you’ve seen examples of chords in real life! In the following sections, we will unfold the definitions, properties, and special characteristics of chords in a circle. Brighterly is committed to making math enjoyable and accessible, and we’ve designed this guide to be both informative and engaging for learners of all ages. Whether you’re a curious beginner or an aspiring mathematician, there’s something here for everyone. Let’s embark on this mathematical adventure together!
What Is a Chord of a Circle?
A chord of a circle is a straight line that connects two points on the circumference of the circle. Just like the spokes of a bicycle wheel, chords can take various lengths and angles. But how does this fascinating geometrical concept relate to the basic definitions of circles and chords? And what makes some chords so special? Let’s explore together!
Definition of a Circle
A circle is a simple shape consisting of all the points in a plane that are equidistant from a fixed point known as the center. The distance from the center to the points on the circle is called the radius. A circle is a symmetrical figure, and you can find it everywhere, from the sun to the wheels of your bicycle. It’s a fundamental concept in geometry, and understanding it lays the foundation for exploring chords.
Definition of a Chord
A chord is a segment whose endpoints lie on a circle. It can be long, short, horizontal, vertical, or diagonal. It’s like a bridge connecting two points on the circle’s edge. In the world of geometry, chords play a vital role in constructing and understanding various shapes and structures within a circle.
Properties of Chords in a Circle
Chords have some fascinating properties within a circle:
 Chords equidistant from the center are equal in length.
 Chords that intersect within a circle divide each other proportionally.
 The angle subtended by a chord at the center is twice the angle subtended by it at any point on the remaining circumference.
These properties help in understanding the behavior of chords and their relationship with other geometric elements in the circle.
Special Chords in a Circle (Diameter, Radius)
Special chords include the diameter, which is the longest chord in a circle, and the radius, which is half the length of the diameter. These unique chords are pivotal in various geometric theorems and concepts like Thales’ Theorem.
Difference Between Chord and Other Segments (Diameter, Radius, Arc, Secant, Tangent)
Chords differ from other segments in the circle, such as:
 Diameter: A chord that passes through the center.
 Radius: Half the length of the diameter.
 Arc: Part of the circumference between two points.
 Secant: A line that intersects the circle at two points.
 Tangent: A line that touches the circle at just one point.
Understanding these differences helps to distinguish various geometric aspects of a circle.
Formulas Associated with Chords in a Circle
The study of chords leads to various formulas:
 Length of a Chord: $L=2⋅r⋅sin(2θ )$, where $r$ is the radius and $θ$ is the angle subtended by the chord.
 Perpendicular Distance from the Center to a Chord: $d=r⋅cos(2θ )$.
Deriving the Formula for Chord Length
The formula for chord length can be derived using simple trigonometry, utilizing the properties of right triangles and the sine function. You can visualize it as two right triangles sharing a common side, and applying the sine function to determine the length of the chord.
Writing Expressions for Chords in a Circle
Expressions for chords can be creatively written using various geometric properties, such as angles, segments, and distances from the center. These expressions help in solving complex problems and understanding the spatial relationships between chords and other elements in the circle.
Practice Problems on Chords of a Circle

The Longest and Shortest Chords: Imagine a circle with a special string that you can slide around inside it. If you make the string go through the very middle of the circle, you create the longest possible chord, called the diameter. Now, move the string around to make different chords. Can you make a chord that is shorter than the diameter? Is there a chord longer than the diameter?

Matching Chords: In a circle, draw two chords of the same length. If you measure how far each chord is from the center, will the distances be the same or different? Try it out with a piece of string and see what you discover!

Chords and Angles: Draw a chord and look at the angle it makes at the center of the circle. Now, move the chord closer to the center without changing its length. What happens to the angle? Is it getting bigger or smaller? Experiment and observe!

Chords as Bridges: Imagine that the circle is a pond, and the chord is a bridge connecting two points on the shore. If you were to walk across different chords (bridges), would some paths be shorter or longer? Can you figure out what makes some chords longer and others shorter?

A Chord Puzzle: Draw two chords that cross each other inside a circle. Use a ruler to measure each part of the chords that the crossing has created. What do you notice about the lengths of the parts that are on the same chord? Are they the same or different?

Special Chord – Halfway Bridge: If you take the longest chord (the diameter) and fold it in half, you get a radius. Can you draw the radius as a chord in your circle? What does it look like? What happens if you try to fold other chords in half?
These engaging problems encourage handson exploration and provide intuitive insights into the nature and properties of chords in a circle. Have fun experimenting, drawing, measuring, and discovering!
Conclusion
The exploration of the chord of a circle has taken us on an enlightening journey through the world of geometry. With Brighterly as your guide, we’ve defined what chords are, explored their properties, differences, special characteristics, and even provided practice problems for you to try out. Understanding chords isn’t just about memorizing formulas; it’s about seeing the connections, patterns, and elegance that geometry offers. At Brighterly, we strive to make learning mathematics a joyful and enriching experience. We believe that curiosity, creativity, and handson engagement lead to deeper understanding. We hope this guide on chords has inspired you to explore further and see the world through the lens of geometry. Thank you for learning with us, and remember, with Brighterly, mathematics is not just numbers; it’s a universe waiting to be explored!
Frequently Asked Questions on Chords of a Circle
What is the difference between a chord and a radius?
A chord connects any two points on the circumference of a circle, while a radius connects the center to a point on the circumference. Think of the radius as a special kind of chord that always reaches the center.
How do I calculate the length of a chord?
Calculating the length of a chord can be done using some formulas, but at Brighterly, we believe in understanding through visualization and experimentation. You can use tools like a ruler, compass, or even software to explore different chord lengths. Our practice problems section offers handson activities to get a grasp of this concept.
Are all chords in a circle the same?
No, chords can vary in length and position. Some chords are special, like the diameter, which is the longest possible chord. Others might be the same length but positioned differently. Explore more with Brighterly to discover the diverse world of chords!
Can chords tell us anything about the circle itself?
Absolutely! Chords can reveal properties of the circle, such as its size and symmetry. By studying chords, mathematicians can solve problems related to arcs, angles, and distances within the circle. It’s like reading a story written in geometric shapes.
Why are chords important in mathematics?
Chords are fundamental in geometry and mathematics. They are involved in theorems, constructions, and even in fields like physics and engineering. Chords are more than just lines; they are bridges to understanding more complex mathematical concepts. Explore more with Brighterly to appreciate the beauty and utility of chords.