Technical Drawing III 5 1 Po l ygon s and a r c l i nk s GALLERY A polygon is a flat shape formed by three or more straight lines that join at points called vertices. The resulting line segments are known as sides. The word polygon is a compound word of Greek origin. It is formed by poly, which means many, and gon, meaning angle. So it is a flat shape with many angles. Classification of polygons Classification of triangles Classification of quadrilaterals Elements of a regular polygon: • Centre (O): the interior point that is the same distance from all of the vertices. It is the centre of the circumscribed and inscribed circumferences of the polygon. • Vertex (V ): the point where two adjacent sides meet. • Side (s): one of the segments that form the polygon. • Radius (r): a segment that connects a vertex to the centre of the polygon. • Apothem (a): a segment that connects the centre to the midpoint of each side. • Diagonal (D): a segment that connects two non-consecutive vertices of a polygon. NUMBER OF SIDES TRIANGLE QUADRILATERAL PENTAGON HEXAGON HEPTAGON OCTAGON NONAGON DECAGON HENDECAGON DODECAGON SIDES EQUILATERAL ISOSCELES SCALENE ANGLES RIGHT-ANGLED ACUTE OBTUSE PARALLELOGRAMS SQUARE RECTANGLE DIAMOND RHOMBOID ANGLES CONCAVE. A polygon that has at least one interior angle of more than 180º. CONVEX. A polygon whose interior angles are each less than 180°. SIDES AND ANGLES REGULAR. A polygon whose sides and angles are equal. IRREGULAR. A polygon whose sides and angles are not equal. AREA OR PERIMETER OPEN. A polygon whose endpoints do not connect at the same point. CLOSED. A polygon whose endpoints connect at the same point. D s V r O a TRAPEZIUMS RIGHT-ANGLED TRAPEZIUM ISOSCELES TRAPEZIUM SCALENE TRAPEZIUM TRAPEZOID
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