Lesson · Grade 4 · Mathematics
Line Symmetry: Folding a Shape Onto Itself
- Grade 4
- Mathematics
- 1 min 19 s
- British Columbia
- BC4-MA-25
A rectangle is folded four ways: down the middle and across the middle make the halves match exactly, but each corner-to-corner fold leaves a corner sticking out, so a rectangle that is not a square has 2 lines of symmetry. A square is then folded the same four ways, every fold matches, so it has 4 lines of symmetry, and the video ends on the recap that a line of symmetry folds a shape so both halves match exactly.
Concept: Line symmetry: lines that fold a shape onto itself
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In one sentence
The question this lesson answers
Where can we fold this rectangle so its two halves match exactly?
Fold it along a line straight down the middle.
Transcript
What the lesson says
Where can we fold this rectangle so its two halves match exactly?
Fold it along a line straight down the middle.
The two halves match exactly, so this is a line of symmetry.
Now fold it straight across the middle.
The halves match again, so that makes 2 lines of symmetry.
What about a fold from corner to corner?
A corner sticks out, so the halves do not match.
The other corner to corner fold does not match either.
So a rectangle that is not a square has 2 lines of symmetry.
Now try a square, which has 4 equal sides.
It matches down the middle and across the middle, just like the rectangle.
This time, both corner to corner folds match too.
So a square has 4 lines of symmetry.
A line of symmetry folds a shape so both halves match exactly.
Curriculum
Where this fits
- British Columbia, Grade 4
Mathematics, Geometry and measurement: line symmetryBC4-MA-25
The outcomes and strands follow the British Columbia curriculum.
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