Primary 4 · Measurement & Geometry
P4 symmetry
A line of symmetry is a fold line: fold the figure along it and the two halves land exactly on each other. In P4, your child spots symmetric figures, tests whether a line is a line of symmetry, and completes symmetric figures on a square grid.
- Taught in
- Term 4
- Syllabus
- 3 skills
- Usual slip
- Equal halves, not mirrored
What your child learns in P4 symmetry
Three skills, each with what it looks like on a worksheet.
See the syllabus wording
- identifying symmetric figures
- determining whether a straight line is a line of symmetry of a symmetric figure
- completing a symmetric figure with respect to a given line of symmetry on square grid
Spot a symmetric figure
A figure is symmetric when it can be folded so the two halves match exactly. Squares, rectangles, kites and letters such as A and M are symmetric. A parallelogram is not.
Test a line by folding
To check a line, fold the figure along it in your head. If the halves land on each other, it is a line of symmetry. Two equal pieces are not enough: a rectangle's diagonal fails the fold.
Complete a figure on a grid
Your child shades squares so a figure matches on both sides of a given line. Each shaded square needs a partner on the other side, the same number of squares away from the line.
Key facts and formulas
- Line of symmetryFold along it: the two halves match exactly.
- Test a lineFold it in your head: do the two halves match? A rectangle has 2 lines of symmetry.
- Complete on a gridEach shaded square has a partner the same distance from the line, on the other side.
Words to know
- Line of symmetry
- A line that splits a figure into two halves that match exactly when folded.
- Fold line
- The line you fold along to test for symmetry.
- Symmetric figure
- A figure with at least one line of symmetry.
- Mirror image
- What each half is of the other, the same shape flipped across the line.
The sentence that costs the mark
Is the diagonal of a rectangle a line of symmetry?
What the working usually does
equal?diagonal=yes
Checks whether it makes two equal pieces. It does, two equal triangles, so this test says yes. It is the wrong test.
What the question asked
matches?diagonal=no
Folds the rectangle along the diagonal and checks whether the halves land on each other. They do not, because the rectangle is longer than it is wide.
The diagonal really does cut the rectangle into two equal triangles, so "equal halves" feels like proof. The only real test is the fold, and along a rectangle's diagonal the halves never meet.
The same P4 symmetry 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 these figures is not a symmetric figure?
- A symmetric figure folds along a line into two halves that match exactly. Check each figure in turn.
- Figure A folds along this line into two matching halves, so it is symmetric.
- A diagonal cuts Figure B into two equal triangles, but no fold makes its halves land on each other. Figure B is not symmetric.
- Figure C is a rectangle. A fold along its diagonal would miss, but it folds along this line through the middle, so it is symmetric.
- So Figure B is the one that is not symmetric.
Every question in StudyLah comes with a walkthrough like this one.
Try it freeTwo quick P4 symmetry questions
Try them together, then tap to check.
Question 1
Which of these letters has a line of symmetry, R, A, S or G?
Show answer
AnswerA. Fold it down the middle and the two halves match. R, S and G have no fold line that works.
Question 2
L is a square. True or false, L has 4 lines of symmetry?
Show answer
AnswerTrue. A square folds four ways, down the middle, across the middle and along both diagonals.
Helping at home
How to tell it has clicked
Hand your child a rectangle of paper and ask them to fold it so the two halves match. They should fold it the short way and the long way, never corner to corner.
Then ask them to fold along the diagonal and look: the corners do not meet. A child who sees that the halves miss knows that equal size is not the same as symmetry.
Try this tonight
Fold a rectangular piece of paper corner to corner. The edges do not line up, so it is not a line of symmetry. Now fold it the short way, then the long way, and both match perfectly.
Try it on a square, a triangle and the letters of your child's name. The rule stays the same: does it fold so the halves land exactly on each other?
Before and after P4 symmetry
Builds on
Primary 1 ShapesNames flat shapes by sides and corners
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Primary 4 Symmetry
Folds figures so the halves match
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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.