Angles is the most fundamental part of geometry, in this session we will understand and learn the definition of various types of angles and their utilization in geometry.

Angle –

Two rays or line segments starting from the same point, form an angle. The common endpoint should be called the vertex of the angle. The rays or line segments are called the arms of the angle. Angles are usually measured in degrees (⁰), and are given names in accordance with their magnitudes, as shown in the following figures.

Adjacent angles –

Two angles are called adjacent angles if they have the same vertex and a common arm and their other arms are on either side of the common arm. In the figure COB and BOA are adjacent angles. 

While COA and COB are not adjacent angles.

Linear Pair –

Two adjacent angles are said to form a linear pair if the sum of their measures is 180⁰. Here AOB & AOC form a linear pair because 115⁰ + 65⁰ = 180⁰


If a ray OA stands on a line BC then the adjacent angles AOB & AOC form a linear pair, that is -

AOB + AOC = 180⁰,

Also, the sum of all the angles at a point of a line on one side of it is 180⁰. Here BOQ + QOP + POC = 180⁰