Common Core Math Vocabulary

Angle - Definition with Examples

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What is an angle? 
In geometry, an angle can be defined as the figure formed by two rays meeting at a common end point.

An angle is represented by the symbol ∠. Here, the angle below is ∠AOB.

angle naming an angle

Angles are measured in degrees, using a protractor. 


Parts of an Angle:

Arms: The two rays joining to form an angle are called arms of an angle. Here, OA and OB are the arms of the ∠AOB.

Vertex: The common end point at which the two rays meet to form an angle is called the vertex. Here, the point O is the vertex of ∠AOB.

parts of an angle arms vertex

We can find angles in various things around us, such as in a pair of scissors, a hockey stick, a chair.

angles in things around us real life example


Types of Angles

Angles can be classified on the basis of their measurements as

- Acute Angles                               - Right Angles                            - Obtuse Angles

- Straight Angles                            - Reflex Angles                           - Complete Angles

Types of angles acute right obtuse straight reflex complete full


Interior and Exterior Angles:

Interior angles: Interior Angles are the angles formed within or inside a shape
Here, ∠ABC, ∠BCA and ∠CAB are interior angles. 

Exterior angles: Exterior angles are the angles formed outside between any side of a shape, and a line extended from the adjoining side. Here, ∠ACD is an exterior angle.

interior and exterior angles

  Fun Facts

  • The word ‘angle’ has been derived from the Latin word Angulus, meaning “a little bending”. 
  • The concept of angle was first used by Eudemus, who defined an angle as a deviation from a straight line. 

let's sing Let's sing!

An acute angle is a little so small,
Right angle in the corner of a wall,
Obtuse angle at 2:50 in day-time,
Straight angle in a straw in soda-lime!
So many angles all around, even in a mime!

let's do it Let's do it!

Instead of handing out geometry angles worksheets to your children, ask your child to observe/spot the things in which they can find different angles such as in a hanger, hands of a clock, or the roof a house.

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