Lecture on Polygons

Definition of a Polygon

• A polygon is a category of shapes.
• Characteristics of a polygon include:
  • Closed figure
  • Straight sides
  • At least three sides

Understanding Closed Figures

• A closed figure doesn’t have openings.
  • Example: A rectangle is closed; liquid can’t be poured into it.
  • An open shape misses a side, like a cup.

Straight Sides

• A polygon must have straight sides.
  • Shapes with curved sides, like circles, are not polygons.

Number of Sides

• A polygon must have three or more sides.
  • Examples:
    • Triangle: 3 sides
    • Quadrilateral: 4 sides
    • Pentagon: 5 sides
    • Shapes can have any number of sides (6, 7, 8, etc.) as long as they are closed with straight sides.

Classification of Polygons by Number of Sides

• Triangles: 3 sides
• Quadrilaterals: 4 sides
• Pentagon: 5 sides
• Hexagon: 6 sides
• Heptagon: 7 sides
• Octagon: 8 sides
• Nonagon: 9 sides
• Decagon: 10 sides

Regular vs. Irregular Polygons

• Regular Polygons
  • Congruent sides and angles
  • Example: Regular hexagon, equilateral triangle, square
• Irregular Polygons
  • Different side lengths and angles
  • Examples: Irregular triangles, irregular pentagons

Examples

• Regular Triangle: All sides and angles are equal.
• Irregular Triangle: Different side lengths and angles.
• Regular Quadrilateral: A square; all sides and angles are equal.
• Irregular Quadrilateral: Rectangle, trapezoid, parallelogram.
• Regular vs. Irregular Hexagon: Regular has equal sides; irregular does not.
• Comparison across other polygons like heptagons, octagons, nonagons, and decagons in regular and irregular forms.

Review

• Polygons are closed shapes with three or more straight sides.
• Regular polygons have equal sides and angles; irregular ones do not.
• Naming of polygons is based on the number of sides they possess.

---

• Note: This video is created by La Fontaine of Knowledge. For more resources and materials, follow the provided links.