2D Shapes and their secrets
You already know circles, squares and triangles. Now count their sides and corners, meet the pentagon family, build new shapes, and fold to find symmetry.
1 · Count sides and vertices
Every flat shape is made of sides (straight lines) and vertices (corners where two sides meet). One corner is a vertex, two or more are vertices. Here is a trick: if a shape has 4 sides, it always has 4 vertices too!
Remember the family: the name tells you the number! Penta means 5, hexa means 6, octa means 8. An octagon has 8 sides — you see one every day on the red STOP sign. And bees build their honeycombs from hexagons, because hexagons fit together with no gaps.
2 · Regular or not regular?
A shape is regular when all its sides are the same length AND all its angles are the same. A square is a regular shape. But a rectangle is not regular — its sides are two different lengths, even though its angles are equal. Both are still quadrilaterals (4-sided shapes), just like you and your friend are both humans even if one of you is taller!
4 equal sides, 4 equal angles Rectangle — not regular
2 long sides, 2 short sides
3 · Build new shapes (compose!)
Shapes are like building blocks. Put two triangles together and you can make a square. Put two squares side by side and you make a rectangle. Cutting a shape into smaller ones is called decomposing; putting pieces together is composing. Architects and designers use this every day — a floor made of wooden boards is just lots of rectangles composing a big shape!
make 1 square
4 · Symmetry: the fold test
A shape has a line of symmetry when you can fold it in half and both halves match exactly, like a mirror. Try it with paper! A square has 4 lines of symmetry. A rectangle has only 2 — folding it corner-to-corner does not match. A circle is the champion: it has endless lines of symmetry, because every fold through the middle matches perfectly.
Quick check
Loading…