🔢 MathGrade 3Lesson 26
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Classify Triangles and Quadrilaterals

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Learning Objectives

  • 1Classify triangles by side lengths and angles
  • 2Identify and name quadrilaterals by their properties
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Mini Lesson

Triangles and quadrilaterals can be sorted into different types based on their side lengths and angles. Knowing the properties of each type helps us identify and name them correctly.

Types of Triangles

  • Equilateral triangle: all 3 sides equal, all 3 angles equal (60 degrees each).
  • Isosceles triangle: exactly 2 sides equal, 2 base angles equal.
  • Scalene triangle: no sides equal, no angles equal.
  • Right-angled triangle: has exactly one 90-degree angle.

Types of Quadrilaterals

  • Square: 4 equal sides, 4 right angles.
  • Rectangle: opposite sides equal and parallel, 4 right angles.
  • Rhombus: 4 equal sides, opposite angles equal, no right angles.
  • Trapezium: exactly 1 pair of parallel sides.
  • Parallelogram: 2 pairs of parallel sides, opposite sides equal.
Three triangle types side by sideThree triangles: equilateral with 3 tick marks on all sides, isosceles with 2 tick marks, and right-angled with a square corner marker.Types of TrianglesEquilateral3 equal sidesIsosceles2 equal sidesRight-angled1 right angle
Four quadrilateral types in a two by two gridFour quadrilaterals: square, rectangle, rhombus, and trapezium, each labeled with its key property.Types of QuadrilateralsSquare4 equal sides, 4 rightRectangleOpposite sides equalRhombusTrapezium
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Tick marks on sides show equal lengths. A square corner marker shows a right angle.

Vocabulary
Triangle
A polygon with 3 sidese.g. A triangle has 3 sides and 3 angles.
Quadrilateral
A polygon with 4 sidese.g. A square is a quadrilateral.
Equilateral
Having all sides the same lengthe.g. An equilateral triangle has 3 equal sides.
Isosceles
A triangle with two equal sidese.g. An isosceles triangle has two sides the same.
Rectangle
A quadrilateral with 4 right anglese.g. A rectangle has 2 long sides and 2 short sides.
Rhombus
A quadrilateral with 4 equal sidese.g. A diamond shape is a rhombus.
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← Lesson 25: Identify Polygons and AnglesLesson 27: Recognize Symmetry and Patterns →