Look around your classroom — the blackboard is a rectangle, the clock face is a circle, and a sandwich cut diagonally becomes a triangle. Geometry is everywhere!
Key Shapes and Their Properties
2-D (flat) shapes lie on a flat surface. They have length and width but no thickness.
- Triangle — 3 sides, 3 corners (vertices)
- Square — 4 equal sides, 4 right-angle corners
- Rectangle — 4 sides, opposite sides equal, 4 right-angle corners
- Circle — no straight sides, no corners, perfectly round
- Pentagon — 5 sides, 5 corners
- Hexagon — 6 sides, 6 corners
A corner of a shape is also called a vertex (more than one = vertices). A side is a straight line that forms the boundary of a shape.
3-D (solid) shapes
3-D shapes have length, width, and height.
- Cube — 6 square faces, 8 vertices, 12 edges (e.g., a dice)
- Cuboid — 6 rectangular faces, 8 vertices, 12 edges (e.g., a brick)
- Sphere — perfectly round, 0 edges, 0 vertices (e.g., a ball)
- Cylinder — 2 circular faces, 1 curved surface (e.g., a can)
- Cone — 1 circular base, 1 apex/tip (e.g., an ice-cream cone)
How many sides does a hexagon have?
A hexagon has 6 sides — think of a honeycomb cell.
Name the 3-D shape that has no flat face.
A sphere has no flat face and no edges.
A shape has 4 equal sides and 4 right angles. What is it?
All 4 sides are equal AND all angles are right angles — it is a square.
Count the faces of a cube.
A cube has 6 faces (top, bottom, front, back, left, right).
A book looks like which 3-D shape?
A book is a cuboid — it has 6 rectangular faces.
Key Formula
Perimeter of a shape = total length of all its sides added together.
Common mistakes
- Students often mix up square and cube. A square is flat (2-D); a cube is solid (3-D).
- A circle has 0 sides and 0 vertices, not 1.
Summary
2-D shapes are flat; 3-D shapes are solid. Count sides and corners to identify 2-D shapes. Count faces, edges, and vertices to identify 3-D shapes.