Primary 3 · Measurement & Geometry
P3 angles
In P3, your child learns that an angle is the turn between two arms that meet at a point. They compare angles with a right angle, the square corner. The size of an angle is how wide it opens, never how long the arms are drawn.
- Taught in
- Term 3
- Syllabus
- 2 skills
- Usual slip
- Judging by arm length
What your child learns in P3 angles
Two skills, each with what it looks like on a worksheet.
See the syllabus wording
- concepts of angle
- right angles, angles greater than/smaller than a right angle
What an angle is
An angle is the turn between two arms that meet at a point, called the vertex. Its size is how wide the arms open. Drawing the arms longer does not make the angle bigger.
Smaller or bigger than a right angle
A right angle is a square corner. Your child checks other angles against it, often with the corner of a sheet of paper. Papers call a smaller angle acute, and a bigger one obtuse.
Key facts and formulas
- An angleTwo lines that meet make an angle. The bigger the turn, the bigger the angle. Longer lines do not make it bigger.
- Right angleA right angle is a square corner, like the corner of a book.
- Acute angleSmaller than a right angle.
- Obtuse angleGreater than a right angle.
Words to know
- Angle
- The turn between two arms that meet at a point.
- Vertex
- The point where the two arms of an angle meet.
- Right angle
- A square corner, like the corner of a book.
- Acute angle
- An angle smaller than a right angle.
- Obtuse angle
- An angle bigger than a right angle.
The sentence that costs the mark
Two angles have the same opening, but one is drawn with longer arms. Which is bigger?
What the working usually does
judge byarm length=bigger
The longer arms fill more of the page, so that angle looks bigger. But arm length is not the angle.
What the question asked
judge bythe opening=equal
The opening between the arms is the same in both, so the angles are equal.
The long-armed angle really does take up more space, so "bigger" feels right. But an angle is the turn between the arms. Look only at the corner where they meet.
The same P3 angles question, worked properly
Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.
Which of the marked angles is a right angle?
- A right angle is a square corner, like the corner of a page. Check each of the four angles against it.
- ∠b and ∠c are both smaller than a square corner, so neither is the one.
- ∠d opens wider than a square corner, so it is not the one.
- ∠a is turned on the grid, so it does not look like a page corner. But its arms meet in a square corner.
- So the right angle is ∠a.
Every question in StudyLah comes with a walkthrough like this one.
Try it freeThree quick P3 angles questions
Try them together, then tap to check.
Question 1
Two of the marked angles are smaller than a right angle. Name them.
Show answer
Answer∠p and ∠q. Both are narrower than a square corner. The other four open wider than one.
Question 2
In the figure below, how many of the marked angles are obtuse?
Show answer
Answer3. ∠d, ∠e and ∠f open wider than a square corner. ∠a, ∠b and ∠c are smaller.
Question 3
Look at the figure below. Which of the marked angles is acute?
Show answer
Answer∠c. It is the only marked angle smaller than a square corner. ∠d, ∠e and ∠f all open wider.
Helping at home
How to tell it has clicked
Draw two angles with the same opening, one with long arms and one with short. Ask which is bigger. A child who says they are the same has it. One who picks the long-armed one is judging by the lines.
Turn the page so a right angle is tilted. If your child still finds it with a paper corner, they are checking the opening, not looking for an upright corner.
Try this tonight
Open a small pair of scissors a little, then a big pair by the same amount. The gap at the pivot is the same, so the angle is the same, even though one pair is longer.
Fold a scrap of paper twice to make a square corner. Use it to test corners around the house: a book, a tile, a door. Is each one smaller, bigger, or the same?
Before and after P3 angles
Builds on
Primary 2 Shapes and PatternsNames the cube, cuboid, cone and cylinder
You are here
Primary 3 Angles
Compares angles with a square corner
Leads to
Primary 3 Perpendicular and Parallel LinesSpots and draws parallel and perpendicular lines
Leads to
Primary 4 AnglesNames, measures and draws angles in degrees
More in Primary 3
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See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.