Center of Circle – Definition, Formula, Examples

Welcome, bright learners! Here at Brighterly, we’re all about breaking down complex mathematical concepts into easy-to-understand, engaging content that fuels your thirst for knowledge. We firmly believe that a strong understanding of the fundamentals can open up a world of possibilities in mathematics and beyond.

Today, we’re excited to explore one such fundamental concept in geometry — the Center of a Circle. This seemingly simple concept serves as the cornerstone for a wide array of topics in both basic and advanced geometry.

So, let’s dive in together and discover the magic of circles, uncover the importance of their center, learn about the formula used to find it, and explore some illustrative examples. Whether you’re a young learner just starting your journey or an eager student looking for a refresher, there’s something here for everyone. Ready to unlock the secrets of the center of a circle? Let’s get started!

What Is the Center of a Circle?

The center of a circle is the exact middle point from which all points on the circle’s edge, or circumference, are equidistant. In simpler words, if you were to draw straight lines from the circle’s center to any point on its circumference, all these lines (known as radii) would be of equal length. This central point is foundational to understanding and applying many mathematical and geometrical concepts.

Understanding the center of a circle can unlock your ability to solve problems related to area, circumference, arcs, sectors, and more. Not only is this knowledge crucial for academic advancement in mathematics, but it also has practical applications in fields such as architecture, design, and engineering.

Center of a Circle: Formula

So, how do we find the center of a circle mathematically? The generic equation for a circle in a two-dimensional space (known as the Cartesian coordinate system) is (x-a)² + (y-b)² = r². Here, (a, b) denotes the center of the circle, and r represents the radius of the circle.

When we talk about formulas involving the center of a circle, we’re typically referring to this equation. This equation is a robust tool that provides us with a reliable method of determining the center of a circle, given that we have the right information.

Equation of a Circle with Center at Origin

A special case arises when the center of the circle is at the origin of the Cartesian coordinate system — that is, at the point (0, 0). In this case, the equation of the circle simplifies to x² + y² = r².

This simplified equation makes it more straightforward to analyze the circle and its properties, particularly in a graphical context. Furthermore, understanding this case can form a stepping stone to understanding more complex geometrical scenarios.

How to Find the Center of a Circle

Now, let’s delve into the specifics of finding the center of a circle in different scenarios.

How to Find the Center of Circle with Two Points?

When a circle is given:

When you have a physical circle — for instance, a coin, a wheel, or a pizza — finding the center can be as simple as using a compass and a straightedge. Drawing two or more chords (straight lines that pass through the circle), and then drawing perpendicular bisectors of these chords, will lead to an intersection point that serves as the center of the circle.

When the equation of a circle is given:

In this scenario, we turn back to our original equation: (x-a)² + (y-b)² = r². The values of a and b in this equation represent the coordinates of the center. Simply identify these values from the equation, and you have your center.

When endpoints of a diameter are given:

If you know the endpoints of a diameter (let’s call these points A and B), you can find the center by finding the midpoint of the line segment AB. Use the midpoint formula: (x1+x2)/2, (y1+y2)/2, and voila — you’ve found the center of the circle!

Solved Examples on Center of a Circle

Mastering the art of finding the center of a circle requires practice. Let’s walk through a couple of examples.

Example 1:

Consider a circle with the equation (x-3)² + (y+5)² = 25.

Here, the center is represented by (a, b) in the equation (x-a)² + (y-b)² = r². Therefore, by comparing, we can see that a=3 and b=-5. Hence, the center of the circle is at the point (3, -5).

Example 2:

Suppose you have a circle with the endpoints of the diameter at A(2, 6) and B(8, 10).

The center of the circle is the midpoint of the diameter. Using the midpoint formula (x1+x2)/2, (y1+y2)/2, we get ((2+8)/2, (6+10)/2) = (5, 8). Therefore, the center of the circle is at the point (5, 8).

Practice Questions on Center of a Circle

At Brighterly, we believe practice makes perfect. Consider the following questions to enhance your understanding:

  1. What is the center of the circle with the equation (x+4)² + (y-3)² = 36?
  2. Find the center of a circle where the endpoints of the diameter are A(-2, -1) and B(6, 3).
  3. If a circle is given with the equation x² + y² – 6x + 8y – 9 = 0, what is its center?


At Brighterly, we are committed to fostering an enriching learning environment that makes seemingly complex mathematical concepts, like the center of a circle, more digestible and engaging. With this understanding, students can unravel a myriad of problems, expanding their capabilities and nurturing their love for learning.

Frequently Asked Questions on Center of a Circle

We understand you may have more questions, so let’s address some commonly asked ones:

What happens if the center of a circle moves?

If the center of a circle moves, it forms a new circle with the same radius but in a different location. The circle’s properties remain unchanged, but its position changes.

Can a circle have more than one center?

No, a circle cannot have more than one center. By definition, the center of a circle is a singular point that is equidistant from all points on the circle’s circumference.

Can the center of a circle be a negative number?

Yes, the center of a circle can be a negative number. The center’s coordinates (a, b) can be either positive or negative, depending on its position in the Cartesian coordinate system.

Information source:
  1. Wolfram MathWorld: Circle
  2. BBC Bitesize: Parts of a Circle
  3. National Council of Teachers of Mathematics: The Center of a Circle

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