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 45^o

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 (90^o) 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 (90^o) 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 (90^o) but is less than 180 degree (180^o) 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 (180^o) 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 (180^o) but is less than 360 degree (360^o) 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 (360^o) or 0 degree (0^o) 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).