How many fold lines?
Is one fold line all a shape can have? No. Some shapes have none. Some have endless fold lines.
Test properly to count properly
Draw many lines through a shape's middle. Fold along each one. Keep the lines that pass, where both halves match. That count is real, not guessed.
| Shape | Fold lines |
|---|---|
| A triangle with three different sides | 0 |
| A triangle with two equal sides | 1 |
| A rectangle | 2 |
| A triangle with three equal sides | 3 |
| A square | 4 |
| A six-sided shape with all sides and all corners equal | 6 |
| A circle | the count never stops |
A circle has endless fold lines. Any line through its centre is one. Test 12 lines — all 12 pass. Test 180 — all 180 pass too.
Watch out!
"More sides must mean more fold lines" — not always. A rectangle has 4 sides and 2 fold lines. A triangle with 3 equal sides has one side fewer. But it has one fold line more.
Turn the dashed line in the lab. Drag it round the shape, or use the slider. See if the fold works. Count the lines that work. Tap Next shape to try another. The circle never runs out of fold lines.
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