# Parallel lines and angles

**Labelling line segments**

A **line segment** is a line with finite length which is shown by end points. The end points are labelled with capital letters.

For example, this line segment

**Lines in a plane**

A **plane** is described as a flat two dimensional surface. There are two types of straight lines in a plane. The first one would be an **intersection** straight line (see below)

The second one is a **parallel,** which are two lines which never meet and are equal distance (equidistant) apart.

**Vertically opposite angles**

In lines where there is an intersection, two two pairs of **vertically opposite angles** are created.

**Perpendicular lines**

In perpendicular lines, two lines intersect at right angles.

**The distance from a point to a line**

The shortest distance from the point to the line is always the perpendicular distance.

**Angles**

**Angles** are formed when two lines meet at a point which is a measure of rotation from one of the line segments to the other. Angle labels are made using lower case letters or Greek letters and in mathematics, a positive rotation is anticlockwise.

** Types of angle**

Types of angles are labelled in the below diagram.

**Angles on a straight line and at a point**

The rules for angles on a straight line and at a point is as follows:

**Complementary and supplementary angles**

Complementary and supplementary angles are described as follows:

**Angles made with parallel lines**

When two parallel lines are crossed by a straight line, eight angles are formed. The crossed line is also called a traversal.

**Corresponding, alternate and interior angles**

The definition of corresponding, alternate and interior angles are as follows: