Plain angle

One of the most important fields of mathematics is known by the name of geometry , a science that is responsible for studying all the properties, shapes and measurements of space or the plane. Within this concept there are many definitions of great importance, one of them is the angles , spaces that exist between the intersection of two different lines. There are many types of angles, in this case, we will talk about the straight angle .

What is a straight angle?

The straight angle, also known as the plane angle , is the portion of the same that is between two rays which are joined by means of a vertex that has an amplitude of 180 °.

  • Definition
  • Characteristics of the shallow angle
  • How much is a straight angle
  • Which objects form a straight angle
  • Examples


The angles are one of the most fundamental parts of mathematics and can also be found in any area where the graphic elements are used. In geometric terms we can define the straight angle as the space that is included in an intersection that occurs between two lines in which there is an opening measuring 180 °.

It can also be defined as the angle that has as sides two rays that are opposite , in other words, that they are collinear . It is also known by the name of rectilinear angle , this because this type of angle is present in straight lines and for this reason, it is in fact the easiest angle to remember.

Characteristics of the shallow angle

The main characteristics of flat angles are the following:

  • The straight angle has an exact measure of 180 ° .
  • It has the ability to form a straight line .
  • Your 180 ° turn will always end in the opposite direction .
  • It is considered as the limit that exists between convex angles and concave angles .
  • It results from the sum that occurs between two right angles .
  • It can be seen as half of a full angle .
  • They have the ability to divide a circle into two equal parts.
  • When the sum is given between an acute angle and an obtuse angle is equal to the measure of the straight angle, then these will become supplementary angles .
  • When you change your address , it will always be to the opposite side.

How much is a straight angle

A straight angle has a measure of 180 ° and in order to measure it you need to use a protractor . It is possible to find this type of measuring instrument with an amplitude of the same measure that the flat angles have.

The way to measure it is very simple, the first thing to do is make a ray with the protractor, then the compass is opened from the origin until reaching the end of the ray and then a 180 ° turn must be drawn until reaching to the opposite side.

If you need to measure the bisector of the straight angle, this turns out to be a quieter procedure because at first glance, the 180 ° angle is a straight line, so you only need to determine its central point , the vertex of the two rays and then start to draw from that place a line perpendicular to both.

Which objects form a straight angle

Some objects that can be found in daily life that form flat angles we mention the following:

  • They can be observed in analog clocks when the hands of the clock form the time.
  • When the arm is stretched or when the dancers make movements with their legs, flat angles can be formed.
  • The horizon, whose opening is described by the curve produced by the sun.
  • In the seesaws that children use to play, a flat angle can easily be observed.
  • When the arm is fully stretched, this type of angle is formed.


Other examples of straight angle are mentioned below:

  • A table
  • Half a watermelon
  • A line drawn with a straight line
  • A wall

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