# Angle & Types of angles

### What is angle?

In the figure the gap between the two lines (OA & OB) or rays is called an angle

The common point at which the lines (OA & OB) intersect is called the vertex

The two lines (OA & OB) are called the arms

The symbol is used to represent angles.

In the example the angle between the two lines (OA & OB) is represented as AOB

In AOB the vertex O should be in the middle

Angle is measured with the unit degree (o). Example: If AOB is 45 degree then it is represented as 45o

Real life example: When you open a book the gap between two pages is called angle. The two pages are called rays and the common point is called vertex.

### What is Right Angle?

If the gap between the two lines (OA & OB) or rays is 90 degree (90o) then it is called right angle.

Right angle is marked using symbol.

Real life example: Angle between most palm trees and the earth is right angle. Square and rectangle are formed using right angle.

### What is Acute Angle?

If the gap between the two lines (OP & OQ) or rays is less than 90 degree (90o) then it is called acute angle.

Real life example: Angle between most stairway and floor is acute angle, a pizza slice. In Triangle at least two angles are acute angles.

### What is Obtuse Angle?

If the gap between the two lines (OB & OA) or rays is greater than 90 degree (90o) but is less than 180 degree (180o) then it is called obtuse angle.

Real life example: Angle between the rooftops of most houses or buildings.

### What is Straight Angle?

If the gap between the two lines (OB & OA) or rays is 180 degree (180o) then it is called straight angle.

Real life example: A straight line, ruler, floor of most buildings or a book is opened and both the pages are touching the ground.

### What is Reflex Angle?

If the gap between the two lines (OB & OA) or rays is greater than 180 degree (180o) but is less than 360 degree (360o) then it is called reflex angle.

Real life example: Exterior angle formed by the letter "V" or Exterior angle of a triangle.

### What is Whole Angle?

If the gap between the two lines (OB & OA) or rays is 360 degree (360o) or 0 degree (0o) then it is called whole angle.

Real life example: Closed book, At time 12 (AM or PM) both the hands are on top of one another.

### What is Interior Angle?

Inside of an angle is called interior angle.

The point X is in the interior angle of ( PQR).

### What is Exterior Angle?

Outside of an angle is called exterior angle.

The point Y is in the exterior angle of ( PQR).