Points, Lines, Segments, Angles etc.

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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.


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


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:
Acute-angle.jpg Right-angle.jpg Obtuse-angle.jpg

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)


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