Pairs Of Lines
There are four pairs of lines:
- Intersecting lines
- Parallel lines
- Skew lines
- Perpendicular lines
If we draw two lines in a plane surface, they will either intersect each other at a point or never meet each other at all.
In figure, lines AB and CD intersect each other at a point (O), such lines are called intersecting lines.
In figure, lines AB and CD never meet each other at any point, i.e., they are equidistant from each other at each and every point. Such lines are called parallel lines. Parallel lines AB and CD are
represented as AB || CD. Here, symbol ‘||’ is read as ‘is parallel to’.
Two lines in two different planes that are neither parallel nor intersecting are called skewed lines.
In figure, l and m lie in different planes, so these are called skewed lines.
Two lines in a plane, which intersect each other and form an angle of 90°, i.e., right angle are called perpendicular lines.
In figure, two lines AB and CD intersecting each other form an angle of 90° at point O. So, AB and CD are perpendicular to each other and is written as AB ⊥ CD. Here, symbol ‘⊥’ is read as ‘is perpendicular to’.
Two or more lines that pass through the same point are called concurrent lines and the point of intersection is called the point of concurrency.
In figure, lines l, m, n, and o are concurrent at the point A.