1What symmetry is made of
A fold line, and twins across it
You only need two ideas. Watch each one:
The fold line
An imaginary crease down the middle. Symmetry is about whether a shape would land exactly on itself if you folded it along this line.
Twins across the line
Every point needs a twin. For a shape to fold onto itself, each point on one side must have a matching point the same distance across the line.
2Two ways to build a shape
Copy every bump, or copy none
Say you're drawing a shape with a fold line down the middle. When you add a bump on one side, there are two rules you could follow:
Copy it to the far side
Every bump you draw also pops out on the other side, the same distance across the line.
Leave it where you drew it
A bump shows up only where you put it. The far side never copies it.
3Your turn — grow a symmetric shape
Tap the near side and watch the far side fill itself in
Tap anywhere on the teal half. A bump grows where you tap — and the violet half copies it across the fold line for free. You're only drawing half the shape, but you're getting the whole thing.
4Now break the mirror and fold it
Add a bump to ONE side only — then fold the shape in half 📄
This time you get a switch. Turn the mirror off, add a single bump to the teal side, and it will NOT be copied across. Then press fold and watch the far half swing over to meet the near half. Guess first — then fold.
Guess before you fold
You add one bump to the left side but DON'T mirror it to the right. Then you fold the shape down its middle. Will the two halves line up?