# Points, Lines, Segments, Angles etc.

## Contents

## Points and Lines

**A point** is a specific location in space. A point is drawn as a dot. Often we label a point with some letter. We would say "Point A" for instance.

Above you see three points labeled A, B and C.

**Lines** are something you have seen in Algebra. Straight lines go on infinitely far in both directions. Closely related to the line are rays and line segments.

**A ray** is what we can think of as "half a line". A ray starts at a given point and then goes of to infinity in one direction.

**A line segment** is just a small part of a line. It starts at one point and ends at another.

In the picture above we see the difference between a line, a ray and a segment. The line is the figure at the top. As we can see it goes on for ever. The figure in the middle is a ray. It starts at a point and then moves off to the top-right. The line segment is all the way at the bottom.

### Example showing several line segments and their labels

We will be using line segments a lot in later sections. We will label segments by recording the endpoints. For example:

In this diagram we see several line segments:

- Segment AP is the line segment connecting A and P. Note that we can also call this segment PA.
- Segment AB (or BA if you like) runs vertically.
- Segment BP is the third segment shown.

AM, MB and MP are also segments. There is also a line in this picture. It is labeled r.

### Worksheet

Do the following Lines and Line Segment Worksheet to check that you have remembered what lines and segments are.

## Angles

An Angle is a shape formed by two rays (or two line segments) that meet at a point. We will measure the size of the angle by using degrees. Here are some examples:

The right angle shown in the middle is a special case. If two segments or lines meet at a 90 degree angle we say they are **perpendicular**. In general we have the following cases:

**Right angle**- exactly 90 degrees**Acute angle**- between 0 and 90 degrees. (the example shown measures 55 degrees)**Obtuse angle**- between 90 and 180 degrees (the example here is 140 degrees)

When we write about angles we can use two different types of notation. They are both acceptable:

- <ABC : The letter in the middle always gives the location of the point where the segments meet. B is called the
**vertex**. - <B : Sometimes we just write the letter of the vertex of the angle.

## Resources

Ouside source: [| Math League: Basic Terms] Click on the link and look at the examples.