What is the standard equation of a sphere?

I can find the ellipsoid, paraboloid, and hyperboloid standard equation but, all I can find out about the sphere is the volume. It doesn't even mention the equation on wikipedia: Sphere - Wikipedia, the free encyclopedia. Does anyone know the standard equation for it?

is a sphere centred at the origin with radius

Cool thanks for the quick reply, one more thing, for (x-h)^2 + (x-k)^2 (z-?)^2 = r^2 what would be the typical letter for the "?"?

Any letter can be used... I would probably use something close to ...


Many texts write the standard equation for a sphere as

@Prove It: So there is no typically accepted way? Ok, then thanks. Just wondering because, I know, for example, that y = mx + b can be substituted with any letters but, by convention we use y, m, x, and b.

See my edit...

The general equation for a sphere

Whether you write the equation as or or you should include the information that the point (a, b, c) (or (h, k, j) or [itex](x_0, y_0, z_0) is the center of the circle and that r is the radius.

You say you found the equations for ellipsoid, paraboloid, and hyperboloid (of one or two sheets?). What convention did they use for the center?

Quote:

---

Originally Posted by thyrgle

@Prove It: So there is no typically accepted way? Ok, then thanks. Just wondering because, I know, for example, that y = mx + b can be substituted with any letters but, by convention we use y, m, x, and b.

---

In Mathematics you will find letters at the beginning of the alphabet a,b,c,etc represent constants while at the other end x,y,z represent variables.

With the case y=mx+b the m represents the gradient which is a special type of constant.