# Parallel

Two or more lines are said to be parallel if they are in the same plane, but never intersect. Two or more planes are parallel if the planes never intersect.

- For two straight lines defined as:
- and
- If
*m*_{1}=*m*_{2}the lines are parallel. - If
*m*_{1}**m*_{2}=-1 the two lines are perpendicular.

**See also: **Corresponding Angles.

**Subjects: ** Geometry