What are Polygons?
 A Polygon is a closed figure made up of lines segments (not curves) in twodimensions.
 A minimum of three line segments are required for making a closed figure, thus a polygon with minimum of three sides is known as Triangle.
Classification of Triangles
In our article on Geometric Shapes, we discussed about the polygons with least number of sides – the Triangle. In this section, we will go through different types of triangles.
 Equilateral triangle – Having all sides equal.
 Isosceles triangle – Having any 2 sides equal.
 Scalene triangle – All 3 unequal sides.
 Acute angled Triangle – Each angle is less than 90^{0}
 Right Angled Triangle – Any one angle is 90^{0}
 Obtuse Angled Triangle – Any one angle is greater than 90^{0}
An Activity:

An interesting facts about Triangle:

Quadrilaterals
A Quadrilateral is a polygon having number of sides equal to four.
The table below gives the comparison of Opposite sides, angles and diagonals of different Quadrilateral.
Quadrilateral 
Opposite 
Sides 
All sides Equal 
Opposite angles equal 

Diagonal 
Parallel 
Equal 
Equal 
Perpendicular 

Rectangle 
✔ 
✔ 
✖ 
✔ 
✔ 
✔ 
Parallelogram 
✔ 
✔ 
✖ 
✔ 
✖ 
✖ 
Rhombus 
✔ 
✔ 
✔ 
✔ 
✖ 
✔ 
Trapezium 
✖(Only one side) 
✖ 
✖ 
✖ 
✖ 
✖ 
Square 
✔ 
✔ 
✔ 
✔ 
✔ 
✔ 
Polygon: A general comparison
Polygon 
No. of Sides 
No. of Diagonal 
No. of vertices 
Interior Angle 
Triangle 
3 
0 
3 
60 
Quadrilateral 
4 
2 
4 
90 
Pentagon 
5 
5 
5 
108 
Hexagon 
6 
9 
6 
120 
Heptagon 
7 
14 
7 
128.571 
Octagon 
8 
20 
8 
135 
Nonagon 
9 
27 
9 
140 
Decagon 
10 
35 
10 
144 
Hendecagon 
11 
44 
11 
147.273 
Dodecagon 
12 
54 
12 
150 
Triskaidecagon 
13 
65 
13 
158.308 
Tetrakaidecagon 
14 
77 
14 
154.286 
Pentadecagon 
15 
90 
15 
156 
Three Dimensional Shape (3D shape)
 These are the shapes that can be projected on a piece of paper but cannot be drawn on a paper. These shapes are known as solids.
2D shape (Polygon) 
3D Shape 
Edge 
Edge 
Vertices 
Vertices 
— 
Faces 
 3D shapes have Faces as the distinguishing Feature.
To know more about polygons, types of polygons and 3D shapes, download Byju’s the Learning App.