Angle definition

Description of angles definition and relationships

Angle definition

An angle is a figure formed by two rays that have the same endpoint. The common endpoint is the vertex of the angle.

  • An angle that measures greater than 0 °, but less than 90 ° ist, is an acute angle

  • An angle that measures greater than 90 °, but less than 180 ° is an obtuse angle

  • An angle that measures 90 ° is a right angle

  • An angle that measures 180 ° is a straight angle

to determine an angle measure in degrees, you can use a protractor. The mathematical symbol to indicate a degree measure is °.


Certain pairs of angles have special relationships. These relationships are useful in determining unknown angle measures. The following sections discuss some of these angle pair relationships.

  • When the sum of the measurements of two angles equals 90 ° the angles are considered complementary.

  • When the sum of two angles is 180 °, the two angles are considered supplementary.

  • Two angles that have a common vertex and a common side are adjacent angles