Pairs of Lines

Pairs Of Lines

There are four pairs of lines:

  1. Intersecting lines
  2. Parallel lines
  3. Skew lines
  4. 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.

Intersecting lines

In figure, lines AB and CD intersect each other at a point (O), such lines are called intersecting lines.
Intersecting-lines

Parallel 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’.
Parallel-lines

Skewed lines

Two lines in two different planes that are neither parallel nor intersecting are called skewed lines.
Skewed-linesIn figure, l and m lie in different planes, so these are called skewed lines.

Perpendicular lines

Two lines in a plane, which intersect each other and form an angle of 90°, i.e., right angle are called perpendicular lines.
Perpendicular-linesIn 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’.

Concurrent lines
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.
Concurrent-linesIn figure, lines l, m, n, and o are concurrent at the point A.