Page 154 - New Medley 5 Semester 2

Competencies
7 Polygons and Circles
C-2.1, C-2.2, C-2.3, C-2.4, C-4.1

Polygons

The shapes made in a plane only with the line segments are called polygons.

These are closed curves. At least three points not in a line are sufficient

to make a polygon. Polygons are named according to the number of sides
they have. Some common polygons are given below.

Triangle Quadrilateral Pentagon Hexagon
(a three-sided (a four-sided (a five-sided (a six-sided

polygon) polygon) polygon) polygon)
Note that a polygon is made with two words ‘poly’ means many and ‘gon’

means angle (or side). Thus, a polygon can have a number of sides and angles.

The polygon having all the sides equal to each other is called regular
polygon. A regular polygon also has equal measure of angles.

Triangles

A triangle is a polygon formed with three line segments. The line segments
that form a triangle are called its sides.

In the adjoining figure, AB, BC and AC are the three A
sides of the triangle ABC. The triangle ABC is written in
symbol as ∆ABC, where A, B and C are three vertices.

∠ABC, ∠BCA and ∠CAB are three angles of ∆ABC.
This triangle can be written in symbol with any order

of its vertices, e.g., ∆ABC, ∆BCA, ∆CAB, ∆ACB, ∆BAC
or ∆CBA. (Six ways) B C

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