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Grade 4 · Maths · Lessons
The folding line
🦋butterfly🪞mirror✂️fold🔷shape
Symmetry.
The big ideaA fold line makes two halves that match exactly.

How it works

A fold line makes two halves that match exactly.

A shape with a fold line has line symmetry.

A rectangle has two fold lines, but its diagonals aren't fold lines.

Fold lines• down the middle• across the middleNot fold lines• corner to corner• off to one side
Fold lines of a rectangle.

Example 1: Do the halves match?

  1. Cut a rhombus along a diagonal.
  2. Fold it and the halves land on each other.
  3. Yes, the halves match.

Example 2: A fold line

  1. Fold a rectangle down the middle.
  2. The two halves match.
  3. That line is a fold line.

Example 3: Not a fold line

  1. Fold a rectangle corner to corner.
  2. The corners don't land on each other.
  3. That line is not a fold line.

Words to know

line of symmetry
A fold line where the halves match.
symmetrical
Having a fold line that makes matching halves.

Watch out

Try it

  1. Does a fold line make two matching halves?
  2. How many fold lines does a rectangle that isn't a square have?
  3. Is the diagonal of a rectangle a fold line?
  4. What do we call a shape with a fold line?
Answers: 1. yes · 2. 2 · 3. no · 4. symmetrical
For grown-upsFold paper shapes and cut them to see which have matching halves.
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