Polygons
Chapter Name : Understanding Quadrilateral |
Sub Topic Code : 104_08_03_02_03 |
Topic Name : Polygons |
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Sub Topic Name : Convex And Concave Polygons |
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Introduction
If a crescent moon is sketched as a polygon of say, 10 sides, it would form a concave polygon. Technically, when all the vertices point outside, its called convex polygon. But even if one points inside, its called concave polygon.
Pre-Requisites:
Basic knowledge about polygons
Activity:
If the line joining two pins lies completely inside the plane surface of the polygon, it is a convex polygon. If at least one line crosses the boundary, it is a concave polygon.
Real Life Question:
What is the shape of a star?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Concave Polygon | At least one vertex points inward |
| Polygon | A simple closed curve classified according to number of sides and vertices |
| Convex Polygon | All vertices point outward |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Scissors, paper, sketches, pins | Polygons are drawn on the paper as plane surfaces, increasing one vertex and a side at a time. Different shapes are formed. Use two pins to indicate points inside the surface and try joining them. |
Real life uses :
Computer screens, TV screens, Joints, Road junctions, stools, scramble puzzles can be classified into concave or convex polygons.
Practical examples around us
| Examples | Explainations |
|---|---|
| T-joints | The T-joints are wrenches. They are used to tighten and loosen the screws on a pair of roller skates. They form concave polygons. |
| Computer monitors | The screen is a convex polygon. Any two points on the screen can be joined by lines on the screen itself. |
What you learn in Theory:
An Intro into convex and concave types of polygons.
What you learn in Practice:
Depending on how two points inside the plane surface can be connected and the position of vertices, the polygons are divided into convex and concave types.