3 min read Jun 17, 2024

Understanding the Equation of a Sphere: (x-h)^2 + (y-k)^2 + (z)^2 = r^2

The equation (x-h)^2 + (y-k)^2 + (z)^2 = r^2 represents the standard form of the equation of a sphere in three-dimensional space. This equation helps us define and understand the key properties of a sphere, including its center and radius.

What does each component represent?

  • (x, y, z): This represents the coordinates of any point on the surface of the sphere.
  • (h, k, l): This represents the coordinates of the center of the sphere.
  • r: This represents the radius of the sphere.

Deriving the Equation

The equation is derived from the distance formula. Imagine a sphere with its center at point (h, k, l). Any point (x, y, z) on the surface of the sphere is a fixed distance r (the radius) from the center. Using the distance formula, we can write:

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

Squaring both sides, we get:

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

This is the standard form of the equation of a sphere.

Key Applications

This equation is crucial in various mathematical and scientific applications:

  • Geometry: It allows us to describe and analyze the properties of spheres, including their volume, surface area, and intersections with other geometric shapes.
  • Physics: It's essential in describing physical phenomena involving spheres, such as gravitational fields, wave propagation, and the movement of celestial bodies.
  • Computer Graphics: It's used in computer graphics to create and render realistic 3D objects.


Let's consider the equation (x - 2)^2 + (y + 1)^2 + (z - 3)^2 = 9. This equation represents a sphere with:

  • Center: (2, -1, 3)
  • Radius: 3 (since the square root of 9 is 3)


The equation (x-h)^2 + (y-k)^2 + (z)^2 = r^2 is a powerful tool for understanding and working with spheres. By understanding the components of this equation and its derivation, we can accurately describe and analyze various aspects of spheres in different contexts.

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