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Quadrilaterals

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A window grille is a metal frame. This one is four straight bars, joined at four corners. Not every four-sided tile in the corridor is a square. What do we call the rest?

Figure 1 — four straight sides, joined at four corners.

This is Part I, Chapter 4 of your textbook: Quadrilaterals.

What you will learn

  • Four sides, joined up — what counts, and what does not.
  • The corner total — the four angles always add to 360°.
  • Diagonals — the two lines that join corners that are not neighbours.
  • Five names — trapezium, parallelogram, rectangle, rhombus, square.
  • What a parallelogram must have — matching opposite sides and angles.
  • The diagonals — how they cut each other in half. Some have extra facts.
  • Several names at once — one shape, more than one correct name.
  • Building one — from measurements, not from a rough drawing.

Each lesson has a lab, apart from the checkpoints, summary and quiz. Move the shape yourself and watch each rule stay true.

Jump to lesson

This track

  1. 0 Start here
  2. 1 Four straight sides, joined up
  3. 2 The four angles come to 360°
  4. 3 A line to the corner across
  5. 4 Five names and what each one demands
  6. 5 What a parallelogram gives you
  7. 6 Checkpoint: sides, angles and the family
  8. 7 Diagonals that cut each other in half
  9. 8 A rectangle also has matching diagonals
  10. 9 A rhombus crosses at a right angle
  11. 10 One shape, several names
  12. 11 Building one from measurements
  13. 12 Checkpoint: diagonals, names and building
  14. 13 The big picture
  15. 14 Track quiz

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