Angles

An angle is formed when two rays (lines)
meet at a common end point.
The common end point is called the vertex.
What is an Angle?
  • An angle is formed by two rays meeting at a common end point.
  • It has a vertex and two arms.
  • It is measured in degrees (°).
  • It is denoted by ∠.
Parts of an Angle
Vertex Arm (Ray) Arm
(Ray)
Types of Angles (Based on Measure)
1. ZERO ANGLE
0°
Arms lie on the same line.
2. ACUTE ANGLE
Greater than 0°
but less than 90°
Lesser than a right angle.
3. RIGHT ANGLE
90°
Exactly equal to a right angle.
4. OBTUSE ANGLE
Greater than 90°
but less than 180°
Greater than a right angle.
5. STRAIGHT ANGLE
180°
Arms lie in opposite directions.
Quick Facts
  • An angle is formed by two rays.
  • The common end point is called the vertex.
  • Angles are measured in degrees (°).
  • There are 7 main types of angles.
  • Angles help us to describe turns, tilts and corners in shapes and objects.
  • Right angle is the most important angle (90°).
Angles in Real Life
Open door
Scissors
Clock hands
Roof of house
Table corner
Road turns
6. REFLEX ANGLE
Greater than 180°
but less than 360°
More than a straight angle but less than a complete turn.
Degree (°)
  • An angle is measured in degrees.
  • 1 right angle = 90°
  • 1 straight angle = 180°
  • 1 complete angle = 360°
  • We use a protractor to measure angles.
7. COMPLETE ANGLE
360°
Arms lie on the same line and make a complete turn.
How to Measure an Angle
  1. Place the centre of the protractor on the vertex.
  2. Align the 0° line with one arm.
  3. Read the degree where the other arm crosses the scale.
0° 30° 50° 90°
Angles in Common Shapes
Triangle
  • 3 angles
  • Sum of angles = 180°
Square
  • 4 right angles
  • Each angle = 90°
Rectangle
  • 4 right angles
  • Each angle = 90°
Parallelogram
  • Opposite angles are equal.
  • Adjacent angles add up to 180°.
  • 4 angles
Hexagon
(Regular)
  • 6 equal angles
  • Each angle = 120°
Key Points to Remember
  • An angle has a vertex and two arms.
  • It is measured in degrees (°).
  • There are 7 types of angles.
  • Right angle = 90°, Straight angle = 180°, Complete angle = 360°.
  • Use a protractor to measure angles accurately.
Think & Answer
  1. How many degrees are there in a right angle?
  2. Which angle is greater than a right angle but less than a straight angle?
  3. If a right angle is 90°, what is a straight angle?
  4. If a complete angle is 360°, what is a half angle?
  5. Find the type of angle formed by the hands of a clock at 3:00.
Important Notes
  • The smaller the opening, the smaller the angle.
  • The wider the opening, the larger the angle.
  • Right angle forms the corner of a square and rectangle.
  • Angles are used in construction, design, road turns, sports and daily life.