In this section we will study different types of angles. Understanding the concept of angles is extremely important. They are the base for mensuration and geometry.

**Let us look at them-**

**Angle**: When two rays originate from a same end point they form an angle.

**Acute angle:**When an angle measures between 0° and 90° it is called an acute angle.**Right angle:**When the angle is exactly equal to 90°, it is called right angle.

**Obtuse angle:**When an angle measures between 90° and 180°. It is called an obtuse angle.

**Straight angle:**When an angle measure exactly 180° it is called straight angle.”

**Reflex Angle:**When an angle is greater than 180° but less than 360°.Then it is called Reflex angle.**Full rotation or complete angle:**When the angle is exactly 360° then it is called a complete angle or a full rotation.

**Other Types of Angles**

**Complementary angles:**When the sum of two angles is 90°, Then they are called complementary angles.**Supplementary angles:**When the sum of two angles is 180°, Then they are called supplementary angles.**Adjacent angles:**Two angles are said to be adjacent when they have same vertex and a common arm. Also the non common arm should be on different sides of the common arm.

Here, OB is the common arm.

O is the common vertex.

and OA and OC are the non common sides in different side of common arm.

∠AOB and ∠BOC are adjacent angles.**Linear pair angles:**When the non-common arms of adjacent angles form a line then the angles are called linear pair of angles.

∠AOB and ∠BOC are Linear pair angles and ∠AOB + ∠BOC = 180°**Vertically Opposite Angles:**When two lines intersect each other , two pair of vertically opposite angles are formed.

Let us say,

AB and CD intersect each other at O.

Here ∠AOC and ∠BOD are vertically opposite angles.

and ∠AOD and ∠BOC are also vertically opposite angles.

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