What is Polygon? — Mathematics

Definition 26.4 Primary & Middle School Mathematics · Chapter 26 — Lines and Polygons

A polygon is a closed figure whose border is made of straight segments, its sides; the corner points are the vertices. Polygons are named by their number of sides: triangle ( $3$ ), quadrilateral ( $4$ ), pentagon ( $5$ ), hexagon ( $6$ ), octagon ( $8$ ).

The polygon family (the pentagon and hexagon drawn here are regular: equal sides and equal corners). A circle is not a polygon: its border is not made of segments. — The polygon family (the pentagon and hexagon drawn here are *regular*: equal sides and equal corners). A circle is not a polygon: its border is not made of segments.

Examples

Example 26.5 (Describing a polygon)

A useful game: describe a figure so precisely that a classmate can redraw it without seeing it. “A quadrilateral $ABCD$ with $AB = 5$ cm, the angle at $A$ right, $AD = 3$ cm …” — vocabulary is what makes the message work.

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