The idea, step by step
A square-corner benchmark
A right angle matches a corner of a square or sheet of paper. It is the opening made by a quarter turn.
Angle arms may be long or short. Their lengths do not change the amount of turn between them.
Compare the opening
Place an imaginary square corner at the meeting point. A narrower opening is smaller than a right angle; a wider opening is larger.
The whole picture may be turned. An angle can still be a right angle when its arms are not pointing straight up and across.
A common trap
Calling an angle larger because its arms are longer.
Instead: Compare the opening between arms, not their lengths.
See the thinking
Three openings
Compare B and C with right angle A.
- B opens less than the square corner.
- C opens more than the square corner.
An open book
A book cover opens to match a paper’s square corner. What angle does it make?
- Compare the opening with the benchmark.
- They match exactly.
Check your understanding
Is a quarter turn smaller than, equal to, or larger than a right angle?
Show answer
Equal to a right angle.
A quarter turn makes a square corner.
Your turn
6 questions · Work at your own pace.
Read the questions online
- Which pictured angle is a right angle?
- Which pictured angle is smaller than a right angle?
- Which pictured angle is larger than a right angle?
- Name an object whose corner can help check a right angle.
- One right angle has short arms; another has long arms. Is either angle larger? Explain.
- Is a half-turn opening smaller or larger than a right-angle turn? Explain.
Read the worked solutions
- Which pictured angle is a right angle?
It has a square-corner mark.
A. - Which pictured angle is smaller than a right angle?
Its opening is narrower than A.
B. - Which pictured angle is larger than a right angle?
Its opening is wider than A.
C. - Name an object whose corner can help check a right angle.
Choose a corner known to be square.
Example: a rectangular book or sheet of paper. - One right angle has short arms; another has long arms. Is either angle larger? Explain.
Arm length does not change the angle.
No. They have the same square-corner opening. - Is a half-turn opening smaller or larger than a right-angle turn? Explain.
A half turn equals two quarter turns; a right-angle turn is one quarter.
Larger.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum
Solid-object features; comparing/classifying objects; turns; smaller/larger than a right angle.
Official curriculum source ↗