# Summary

- In three dimensions, the coordinate axes of a rectangular Cartesian coordinate system are three mutually perpendicular lines. The axes are called the
- The three planes determined by the pair of axes are the coordinate planes, called XY, YZ and ZX-planes.
- The three coordinate planes divide the space into eight parts known as octants, in the form of triplet like. Here are the distance from the YZ, ZX and XY-planes.
- Any point on is of the form
- Any point on is of the form
- Any point on is of the form .

- Distance between two pointsis given by
- The coordinates of the point B which divides the line segment joining two points internally and externally in the ratio
*m*:*n*are given by respectively. - The coordinates of the mid-point of the line segment joining two points are
- The coordinates of the centroid of the triangle, whose vertices are are