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Door 16 · Grade 3

📐 Quadrilaterals

All quadrilaterals: 4 sides + 4 angles

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Recognize Quadrilaterals

A quadrilateral is any closed shape with exactly 4 sides and 4 angles.
• Square: 4 equal sides, 4 right angles
• Rectangle: Opposite sides equal, 4 right angles
• Rhombus: 4 equal sides, opposite angles equal (no right angles)
• Trapezoid: Exactly 1 pair of parallel sides
• Parallelogram: 2 pairs of parallel sides, opposite sides equal

Worked example

Problem: Which quadrilateral has 4 equal sides AND 4 right angles?

  1. A square.
  2. It is the only quadrilateral with both properties.

Answer: It is the only quadrilateral with both properties.

A Square is a Special Rectangle

Think of shapes as a family — some shapes belong to more than one group.
• Every rectangle has: 4 right angles + opposite sides equal
• Every square has: 4 right angles + ALL sides equal

Since a square meets all the rules of a rectangle AND has equal sides, every square is a rectangle. But not every rectangle is a square (unless all sides are equal).

Worked example

Problem: Is a square a rectangle?

  1. Yes.
  2. A square has 4 right angles and opposite sides equal — it meets all rectangle requirements.
  3. Plus all sides are equal.

Answer: Plus all sides are equal.