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

3 min read Jun 17, 2024
(x-h)^2+(y-k)^2=r^2 Is Called

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

The equation (x-h)^2 + (y-k)^2 = r^2 is a fundamental formula in geometry, representing the standard form of the equation of a circle. This equation describes all points that are a fixed distance r (the radius) away from a central point (h, k) (the center) of the circle.

Understanding the Equation

  • (x-h)^2 + (y-k)^2: This part represents the distance formula between any point (x, y) on the circle and the center (h, k).
  • r^2: This represents the square of the radius, which is the constant distance from the center to any point on the circle.

Why is it Important?

This equation is crucial in understanding and manipulating circles in various applications:

  • Geometry: This equation provides a direct way to define and graph circles.
  • Analytical Geometry: It allows us to determine the center and radius of a circle given its equation.
  • Calculus: It is essential in finding the tangent lines, areas, and volumes related to circles.
  • Engineering and Physics: Many real-world applications involve circles, such as gears, wheels, and orbits, which rely on this equation for calculations.


Let's say we have a circle with center (2, 3) and radius 5. Its equation in standard form is:

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

This equation tells us that any point (x, y) that satisfies this equation lies on the circle.


This equation can be used to:

  • Find the equation of a circle given its center and radius.
  • Determine the center and radius of a circle given its equation.
  • Translate circles by changing the values of 'h' and 'k'.
  • Scale circles by changing the value of 'r'.

Understanding the equation (x-h)^2 + (y-k)^2 = r^2 is key to working with circles in various mathematical and practical contexts. It provides a concise and powerful representation of these fundamental geometric shapes.

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