Complementary angles are **those angles that together add up to 90 degrees or 90º**.

## Calculation of complementary angles

To calculate the complementary angle of a specific angle you only need to **subtract 90 minus the known angle**, for example, to know the complementary angle of an angle of 65º we must do the following subtraction: 90 – 65 = 25. This means that the complementary angle The angle of 65º is an angle of 25º.

Similarly, adjacent complementary angles are known as those that share a vertex and summed up to give right angles, that is, 90 ° angles.

## Characteristics of complementary angles

It is important to know the complementary angles because they are found in many forms in nature and in physical phenomena. Complementary angles are used in architecture, construction, physiognomy, etc.

Through the knowledge of the complementary angles a spectrum of trigonometric notions is derived, for example, the notion that the sum of the internal angles of a right triangle gives 180 degrees since it is composed of an angle of 90 degrees plus two angles complementary treble which adds up to 180 degrees.

Trigonometry as a study of the relationships between the sides and angles of a triangle should be based on the knowledge of the angles. Triangles are classified in this measure according to the degrees or difference in their sides, for example, a right triangle contains an angle of 90 degrees or a scalene triangle that contains different angles and sides.

The **supplementary angles** other hand, are those angles which together have 180 degrees or 180 degrees. An angle of 180 degrees is called a flat angle.