🔢 MathGrade 4Lesson 26
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Classify Polygons

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Learning Objectives

  • 1Identify and name common polygons
  • 2Sort polygons by number of sides and angles
  • 3Describe properties that distinguish triangles, quadrilaterals, and other polygons
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Mini Lesson

A polygon is a closed flat shape with straight sides. Every polygon has the same number of sides and angles. We name and classify polygons by counting their sides.

Triangles

  • A triangle has 3 sides and 3 angles.
  • Types include equilateral (all sides equal), isosceles (two sides equal), scalene (no sides equal), and right triangle (one 90° angle).
  • The three angles of any triangle always add up to 180°.

Quadrilaterals

  • A quadrilateral has 4 sides and 4 angles.
  • Examples: square (4 equal sides, 4 right angles), rectangle (opposite sides equal, 4 right angles), rhombus (4 equal sides, opposite angles equal), trapezoid (one pair of parallel sides).
  • The four angles of any quadrilateral always add up to 360°.

Other Polygons

  • Pentagon: 5 sides, 5 angles.
  • Hexagon: 6 sides, 6 angles (like a honeycomb cell).
  • Octagon: 8 sides, 8 angles (like a stop sign).
  • A regular polygon has all sides equal and all angles equal.
Common polygons: triangle, square, pentagon, hexagonCommon PolygonsTriangle3 sides, 3 anglesSquare4 sides, 4 anglesPentagon5 sides, 5 anglesHexagon6 sides, 6 angles
Polygon properties tablePolygon PropertiesNameSidesAnglesExampleTriangle33EquilateralQuadrilateral44SquarePentagon55Reg. pent.Hexagon66Reg. hex.Octagon88Stop signRegular polygons: all sides and angles equal
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Tip: count the sides to name the polygon — tri = 3, quad = 4, penta = 5, hexa = 6, octa = 8. Every polygon's sides and angle count are always the same number.

Vocabulary
Polygon
A flat, closed shape with three or more straight sidese.g. A triangle is a polygon.
Quadrilateral
A polygon with exactly 4 sidese.g. A square is a quadrilateral.
Regular polygon
A polygon with all sides equal and all angles equale.g. A regular hexagon has six equal sides.
Vertex
A corner where two sides of a polygon meete.g. A pentagon has 5 vertices.
Side
A straight edge of a polygone.g. An octagon has 8 sides.
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← Lesson 25: Identify Angles and LinesLesson 27: Measure Area and Perimeter →