# Three dimensional coordinate systems. â€‹

additional to x and y axes there is also a z axis in three dimensional coordinate systems.

### Coordinate planes: â€‹

Coordinate planes are planes that pass through two axes.

These are the coordinate planes in three dimensions:

- xz-plane (y = 0)
- xy-plane (z = 0)
- yz-plane (x = 0)

### Distance â€‹

Definition

The distance between the points

### Spheres â€‹

Definition

A sphere with center P and radius

If P = (a,b,c) then (x,y,z) is on the sphere whenever

(the point (x,y,z) is at r distance from p so its in the sphere) This is equivalent to