(x-h)^2+(y-k)^2=r^2 Equation

4 min read Jun 17, 2024
(x-h)^2+(y-k)^2=r^2 Equation

The Standard Form of a Circle: (x-h)^2 + (y-k)^2 = r^2

The equation (x-h)^2 + (y-k)^2 = r^2 represents the standard form of the equation of a circle. This equation provides a concise and powerful way to describe the characteristics of a circle, allowing us to easily determine its center and radius.

Understanding the Components

  • (x, y): Represents any point on the circle.
  • (h, k): Represents the coordinates of the center of the circle.
  • r: Represents the radius of the circle.

How the Equation Works

The equation is based on the Pythagorean theorem, which states that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.

Imagine a circle centered at (h, k) with radius r. If we draw a line from the center to any point (x, y) on the circle, this line will be the radius (r). We can then form a right triangle with this line as the hypotenuse, and the horizontal and vertical distances from the center to the point (x, y) as the other two sides.

The horizontal distance is |x - h| and the vertical distance is |y - k|. Therefore, according to the Pythagorean theorem:

(x - h)^2 + (y - k)^2 = r^2


Let's say we have a circle with a center at (2, 3) and a radius of 5. Using the standard form of the equation, we can write:

(x - 2)^2 + (y - 3)^2 = 5^2

This equation describes all the points (x, y) that lie on the circle with the given center and radius.


Understanding the standard form of the equation of a circle is essential in various fields:

  • Geometry: Deriving the equation of a circle, finding its center and radius, and solving geometric problems involving circles.
  • Calculus: Finding the equation of tangent lines to circles and calculating areas and volumes related to circular shapes.
  • Physics and Engineering: Modeling circular motion, studying wave propagation, and designing circular structures.
  • Computer Graphics: Creating and manipulating circular objects in software applications.

By understanding the standard form of the equation of a circle and its components, you gain valuable tools for analyzing and working with circles in a variety of contexts.