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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?

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.