The idea, step by step
A right angle is a useful benchmark
An angle describes the turn between two rays meeting at a vertex. A right angle is a quarter turn, like a square corner. A smaller opening is acute. An opening larger than a right angle but smaller than a straight turn is obtuse. Compare with a paper corner instead of guessing from side lengths.
Beyond a right angle
A straight angle is a half turn and makes a straight line. A reflex angle is more than a half turn but less than a full turn. When two rays are drawn, say which opening is intended. Longer rays do not make an angle larger; the amount of turn matters.
A common trap
Longer rays mean a larger angle.
Instead: Changing ray length does not change the opening or turn.
See the thinking
A narrow opening
The marked opening is smaller than a square corner. What type of angle is it?
- Use the right angle as a benchmark.
- The opening is smaller, not equal.
A wide opening
An angle is bigger than a right angle but smaller than a straight angle. Name it.
- It is more than a quarter turn.
- It is less than a half turn.
Check your understanding
What is the name of a half-turn angle?
Show answer
A straight angle.
A half turn lies along a straight line.
Your turn
6 questions · 8 marks · Work at your own pace.
Read the questions online
- Name the supplied narrow angle.1 mark
- Name a quarter-turn angle.1 mark
- Name the supplied wide angle.1 mark
- An opening is more than a half turn but less than a full turn. Name it.1 mark
- Two angles have equal openings but one has longer rays. Which angle is larger?2 marks
- Draw an acute angle and an obtuse angle. Label each.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Name the supplied narrow angle.1 mark
Its opening is less than a right angle.
Acute. - Name a quarter-turn angle.1 mark
A quarter turn matches a square corner.
A right angle. - Name the supplied wide angle.1 mark
It is larger than a right angle but smaller than a straight angle.
Obtuse. - An opening is more than a half turn but less than a full turn. Name it.1 mark
Reflex angles are larger than straight angles.
Reflex. - Two angles have equal openings but one has longer rays. Which angle is larger?2 marks
Ray length does not change the turn.
Neither; they are equal. - Draw an acute angle and an obtuse angle. Label each.2 marks
Use a paper corner to check the comparison; no protractor is needed.
Any acute opening smaller than a right angle and any obtuse opening between a right and straight angle.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics 2026
Composite shapes/objects; angle names; reflection/rotational symmetry; creating designs.
Official curriculum source ↗