Understand the idea.
A square-corner benchmark
A right angle matches the square corner of a sheet of paper. It describes the opening made by a quarter turn. Use that familiar corner as a benchmark when comparing other angles.
The angle depends on the opening between its arms. Making an arm longer does not make the turn larger. Moving or rotating the whole picture also leaves the opening unchanged.
Compare the opening
Put the paper corner’s meeting point on the angle’s meeting point, then line up one arm. Compare where the other arm lies. Inside the square-corner opening means smaller; beyond it means larger.
Check the opening marked in the picture, rather than the lengths of the lines. If both arms match the paper corner, the angle is exactly a right angle, even when the drawing is tilted.
See the method in action.
Three openings
Compare B and C with right angle A.
Worked solution
- 1
Use A as the benchmark.
A shows the square-corner opening of a right angle.
- 2
Compare B with A.
B’s marked opening is narrower than the square corner, so B is smaller than a right angle.
- 3
Compare C with A.
C’s marked opening is wider than the square corner, so C is larger than a right angle.
B is smaller than a right angle; C is larger.
An open book
A book cover opens to match a paper’s square corner. What angle does it make?
Worked solution
- 1
Choose the square paper corner as the benchmark.
That corner represents a right angle.
- 2
Compare the book’s opening with it.
The question says the openings match, so neither is smaller or larger.
- 3
Name the angle.
The matching opening means the book cover makes a right angle.
A right angle.
Try it yourself.
Check your understanding
Is a quarter turn smaller than, equal to, or larger than a right angle?
Show answer & reasoning
Equal to a right angle.
A quarter turn is equal to a right angle. Both describe the same square-corner opening, regardless of which direction the angle is facing.
Keep practising
6 worksheet questions
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 ↗