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📐 Mathematics - Class 7
Lesson 2 · Triangle, Quadrilateral and Polygon

Quadrilaterals and Their Properties Presentation

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Unit 2 · Triangle, Quadrilateral and Polygon

Quadrilaterals and Their Properties

Mathematics · Grade 7

What You Will Be Able To Do

🌳

Place any quadrilateral in the family tree and say what extra condition each name adds

🔢

Use the fact that four angles always total 360° to find a missing angle

📐

Derive the parallelogram properties from parallel line facts, not from memory

✂️

Identify a shape from the behaviour of its diagonals alone

The Family Tree

1Quadrilateral: any closed shape with four straight sides
2Add one pair of parallel sides, and it becomes a trapezium
3Add the second parallel pair, and it becomes a parallelogram
4Add equal sides for a rhombus, or right angles for a rectangle
5Add BOTH, and it is a square. So a square is all of the above at once

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Presenter notes: Open with a question that will divide the room. Draw a square on the board and ask, is this a rectangle. Most students will say no, some will say yes, and a few will argue. Do not settle it yet. Tell them that by the end of the lesson everybody will agree on the answer and will be able to say why, and that the reason is not about squares at all but about how mathematical names are built. Leave the square on the board for the whole lesson.