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

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

Understanding the Circle Equation: (x - h)^2 + (y - k)^2 = r^2

The equation (x - h)^2 + (y - k)^2 = r^2 is the standard form for the equation of a circle. This equation might seem daunting at first, but it's actually quite simple to understand and use. Let's break down each component of the equation and explore how it describes the circle.

Understanding the Components

  • (x - h)^2 + (y - k)^2: This part of the equation represents the distance formula in disguise. It calculates the square of the distance between any point (x, y) on the circle and the center of the circle (h, k).
  • r^2: This represents the square of the radius (r) of the circle.

Visualizing the Equation

Imagine a circle centered at point (h, k) with a radius of r. Let (x, y) be any point on the circle. The distance between the center (h, k) and the point (x, y) is the radius (r). We can use the distance formula to express this relationship:

√((x - h)^2 + (y - k)^2) = r

To get rid of the square root, we square both sides of the equation, resulting in:

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

This equation essentially states that the square of the distance between any point (x, y) on the circle and the center (h, k) is always equal to the square of the radius (r).

Applications of the Equation

The circle equation is incredibly useful in various fields, including:

  • Geometry: Determining the center and radius of a circle given its equation, finding the equation of a circle given its center and radius, and solving problems related to circle properties like tangents and chords.
  • Physics: Describing the motion of objects in circular paths, like planets orbiting the sun.
  • Computer Graphics: Representing circular objects and creating smooth curves in computer graphics.


Let's say we have a circle with a center at (2, 3) and a radius of 5. The equation of this circle would be:

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

(x - 2)^2 + (y - 3)^2 = 25

This equation describes all the points (x, y) that are exactly 5 units away from the point (2, 3).


The equation (x - h)^2 + (y - k)^2 = r^2 provides a powerful and concise way to represent circles. Understanding this equation and its components allows us to easily work with circles in various mathematical and real-world contexts.

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