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Engineering Drawing Class 9

Polygons are closed, plane figures bounded by straight lines called sides. There are two types: regular polygons with all sides of equal length and angles of equal measure, and irregular polygons with unequal sides and/or angles. Common regular polygons include squares, equilateral triangles, and hexagons. The interior angles of any polygon sum to (n-2) x 180 degrees, where n is the number of sides. Convex polygons have no interior angles greater than 180 degrees, while concave polygons have at least one interior angle exceeding 180 degrees.

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1K views7 pages

Engineering Drawing Class 9

Polygons are closed, plane figures bounded by straight lines called sides. There are two types: regular polygons with all sides of equal length and angles of equal measure, and irregular polygons with unequal sides and/or angles. Common regular polygons include squares, equilateral triangles, and hexagons. The interior angles of any polygon sum to (n-2) x 180 degrees, where n is the number of sides. Convex polygons have no interior angles greater than 180 degrees, while concave polygons have at least one interior angle exceeding 180 degrees.

Uploaded by

GopiKrishnaValireddy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Geometrical constructions

Polygons:
Polygons are the closed figures which have atleaset
3 sided bounded straightly.
Examples:
Triangles
Quadrilaterals
Pentagons
Hexagon
Heptagon etc..
Regular polygons: which are having all sides equal to
all angles otherwise it is called irregular polygons.
Geometrical constructions
Examples:
1. Square, rhombus are regular polygons
2. Equilateral triangle is a regular polygon
polygons generally two types
1. Convex 2. concave
2. All the polygons are classifies as either convex or
concave.
What is convex polygon?
In a polygon no diagonal travels out side the figure
from one side to other side.
no angle inside the polygon is greater than 180
degrees.
Geometrical constructions
Example for convex polygons:
Geometrical constructions
What is concave polygon?
In a polygon atlease one diagonal travels out
side the figure from one side to other side.
atlease one angle inside the polygon is greater
than 180 degrees.
Exampes figures:
Geometrical constructions
Below table describes name and no of sides of a polygon:

Name of the polygon No of sides

Triangle 3

Quadrilaterals 4

Pentagon 5

Hexagon 6

Heptagon 7

Octagon 8

Nonagon 9

Decagon 10
Geometrical constructions
General formula for interior angles :
Sum of the measure interior angles of a ploygon is (n-2)180
Polygon No of vertices No of angles Interior angles sum

Triangle 3 3 1 x 180 = 180

Quadrilateral 4 4 2 x 180 = 360

Pentagon 5 5 3 x 180 = 540

Hexagon 6 6 4 x 180 = 720

Heptagon or 7 7 5 x 180 = 900


septagon

Octagon 8 8 6 x 180 = 1080

Nonagon 9 9 7 x 180 = 1260

decagon 10 10 8 x 180 = 1440


Geometrical constructions
Exterion angle:The sum of exterior angles of a
polygon is always 360 degrees.
Each angle of a regular polygon:
Formula is (n-2) x 180/n
Where n is no of sides of pllygon.

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