Introduction to Angles
Learn what angles are, how to spot right angles, and the difference between angles that are greater or less than a right angle.
What Is an Angle?
An angle is formed when two straight lines meet at a point. The point where they meet is called the vertex. The size of an angle tells us how much one line has turned from the other.
Two Lines Meeting at a Point
An angle is the amount of turn between two lines that meet at a point.
Right Angles
A right angle is a very important angle. It looks like the corner of a square or the corner of a book. It is exactly a quarter turn.
We mark a right angle with a small square symbol in the corner.
What a Right Angle Looks Like
Right angle
Quarter turn
A square has
4 right angles
The Paper Corner Test
You can check for a right angle using the corner of a piece of paper. Hold the paper corner up to an angle:
- • If the angle fits exactly with the paper corner, it is a right angle.
- • If the angle is smaller than the paper corner, it is less than a right angle (acute).
- • If the angle is bigger than the paper corner, it is greater than a right angle (obtuse).
Types of Angles
We can sort angles into three types by comparing them to a right angle.
Less Than a Right Angle
Smaller, more narrow. Also called an acute angle.
Right Angle
Exactly a quarter turn. Like a square corner.
Greater Than a Right Angle
Wider, more open. Also called an obtuse angle.
Angles in Everyday Objects
Angles are everywhere! Look around you and see how many you can spot.
Right Angles
- • Corner of a book
- • Corner of a door
- • Corner of a window
- • Corners of a TV screen
- • Where a wall meets the floor
Less Than a Right Angle
- • Tip of a pizza slice
- • Hands of a clock at 1 o'clock
- • An open pair of scissors (a little)
- • Corner of a triangle ruler
Greater Than a Right Angle
- • Hands of a clock at 10 o'clock
- • A door opened wide
- • A book lying flat open
- • A reclining chair leaning back
Try This!
Walk around your house or classroom with a piece of paper. Hold the corner up to different angles you find. Can you tell if they are right angles, less, or greater?
Key Vocabulary
Angle
The amount of turn between two lines that meet at a point.
Right Angle
An angle that is exactly a quarter turn, like the corner of a square.
Acute Angle
An angle that is less than a right angle. It looks sharp and narrow.
Obtuse Angle
An angle that is greater than a right angle but less than a straight line. It looks wide.
Vertex
The point where two lines meet to form an angle.
Worked Examples
How many right angles does a rectangle have?
Step 1: A rectangle has 4 corners.
Step 2: Each corner is a right angle (like a square corner).
Answer: A rectangle has 4 right angles.
Is this angle less than, equal to, or greater than a right angle?
Step 1: Compare it to the corner of a piece of paper.
Step 2: The angle is narrower (smaller) than the paper corner.
Answer: This is less than a right angle (an acute angle).
At 3 o'clock, the clock hands form what type of angle?
Step 1: At 3 o'clock, the hour hand points right and the minute hand points up.
Step 2: The hands make a quarter turn.
Answer: It is a right angle (exactly a quarter turn).
Knowledge Check
Select the correct answer for each question.
Question 1
What type of angle is shown below?
Question 2
How many right angles does a square have?
Question 3
What type of angle is this?
Question 4
Which of these would have a right angle?
Question 5
What type of angle is this?
Key Concepts Summary
- ● An angle is formed where two lines meet at a point (vertex).
- ● A right angle is exactly a quarter turn, like the corner of a square.
- ● An acute angle is less than a right angle (smaller, narrower).
- ● An obtuse angle is greater than a right angle (wider, more open).
- ● Use the corner of a piece of paper to test if an angle is a right angle.