Flat Angle – What is it, examples and other types of angles

We explain what a flat angle is in geometry, its characteristics and examples from everyday life. Also, other types of angles.

plain angle
The sides of a straight angle are two continuous rays that intersect at the vertex.

What is a straight angle?

In geometry, plane angles are called those that have a measure of amplitude exactly equal to 180 ° sexagesimal (or in other units to 𝛑 radians or 200g hundredths). This means that it is a very wide angle, more than the obtuse angles, and that its sides constitute two continuous rays that intersect at the vertex.

Since the sides of the angle are two indistinguishable rays, their midpoint is considered the vertex, which is why it is common to also find that they are known as the extended angle or as the right angle.

Another way to understand it is that the rays of the sides start at the vertex and move away in opposite directions, they are interpreted as opposite orientations. That is the reason that in everyday speech we say that someone “made a 180 ° turn” to mean that they radically changed their opinion.

Characteristics of plain angles

Flat angles are characterized by the following:

  • They have a 180 ° opening exact sexagesimals.
  • Its sides are two rays that arise at the vertex and they move away in opposite directions.
  • Equals half a full angle (or circumference) of 360 °.
  • Its sides form a single line with the vertex at their meeting point. For that reason they are also known as “right angles”.
  • Sometimes they are the result of the sum of two right angles (each 90 ° sexagesimal).

Examples of shallow angles

plain angle example
Some ballet poses place the legs at a 180 ° angle.

Some everyday examples of flat angles are:

  • The angle they form the legs of a ballet dancer when extending during a jump (grand jete or stride).
  • If we cut a circumference in half (a cake, for example), we will draw a line that divides it into two flat angles.
  • If we force a book or a notebook to be opened to the maximum until it is flat, we will have forced its caps to form an angle of 180 °.
  • The arms of a cross they draw a flat angle with respect to the trunk that supports them (two 90 ° angles, which when added together yield an angle of 180 °).

Angle types

In addition to plain angles, there are four other classifications of angles:

  • Null angles, whose opening does not exceed 0 °, that is, they are non-existent.
  • Acute angles, whose opening is greater than 0 ° but less than 90 ° sexagesimal.
  • Right angles, whose aperture is exactly 90 ° sexagesimal.
  • Obtuse angles, whose opening exceeds 90 ° sexagesimal, but is less than 180 ° of the shallow angle.