Four straight sides, joined up
Four dots on a page. Join them in order. Do you always get a quadrilateral, a four-sided shape?
Step 1 of 4
- Four dots on the page.
- Join dot 1 to 2, then 2 to 3.
- Join 3 to 4, and 4 back to 1.
- Closed, four straight sides: a quadrilateral.
No. Some ways of joining the dots make two sides cross.
Rule: A quadrilateral needs three things.
- Sides that are straight — no curves, no bends.
- A path that is closed — the last side meets the first.
- No side that cuts through another.
Join the same four dots in a different order. Try top-left, bottom-right, top-right, bottom-left. Two sides now cross in the middle. That shape fails the third rule: no side cuts through another.
A dented shape has one corner pushed inwards. It is still a quadrilateral, because its sides do not cross.
Every corner is where two sides meet. So a quadrilateral always has four corners, to match its four sides.
Drag a dot until two sides cross. Then drag it back.
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