# Icosahedron

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## Icosahedron Meaning

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The icosahedron is one of the five platonic solids bounded by 20 equilateral triangles and has 12 vertices and 30 edges. The word “icosahedron’ is derived from the Greek word Eikosi means ‘twenty’ and hedra meaning ‘ seat’. The plural form of icosahedron means ‘Icosahedra’ or ‘Icosahedrons’.

There are numerous non - similar shapes of Icosahedra, some of the shapes among them being more symmetrical to others. The best non-similar Icosahedra shape is known as (convex, non-stellated) regular icosahedron, a platonic solid whose faces are 20 equilateral triangles. The platonic solids other than Icosahedron are tetrahedron, dodecahedron, cube, and octahedron.

### What is Platonic Solid?

In three - dimensional geometry, a platonic solid is a regular convex polyhedron. It is constructed by congruent (equal shape and size), regular (all sides and angles are equal), polygon faces with the same number of faces meeting at each vertex ( the sum of each angle at vertex is less than 360 degrees).

There are five platonic solids namely Isochaedram, Tetrahedron, Octahedron, cube, and dodecahedron. These five platonic solids represent the five basic elements that are Air, Water, Earth, Fire, and the Universe.

• The cube represents the Earth.

• The Octahedron represents the Air.

• The Tetrahedron represents the Fire.

• The Ichedrom represents the Water.

• The dodecahedron represents the Universe.

### Regular Icosahedron

A regular icosahedron is a convex polyhedron consisting of 20 faces, 30 edges, and 12 vertices. It is one of the five platonic solids, one with the maximum number of faces. Five equilateral triangular faces of the Icosahedron meet each other at the vertex. It is often denoted by  Schläfli symbol {3,5}, or by its vertex figure as 3.3.3.3.3 or 35

The regular icosahedron is a dual of the dodecahedron which is denoted by (5,3), having 3 pentagon faces around each vertex.

### Icosahedron Structure

The definition of the icosahedron is obtained from the Ancient Greek words Icos (eíkosi) meaning 'twenty' and hedra (hédra) meaning 'seat'.

Icosahedron structure is best defined in the following points.

The icosahedron is one of the five platonic solids.

• A regular Icosahedron has 30 edges, 20 equilateral triangles faces, with 5 faces meeting at each of its 12 vertices.

• The icosahedron has the maximum number of faces and volume among all 5 platonic solids for its surface area.

• The number of sides of Icosahedron is 20.

• The volume of Icosahedron is calculated by using the formula

$\frac{5}{12}\times (3+\sqrt{5})\times a^{3}$

### Icosahedron Shape Characteristics

Following are the characteristics of Icosahedron shape:

• The number of faces, edges, and vertices of the icosahedron are 20, 30, and 12 respectively,

• The face type of Icosahedron is a regular triangle.

• The number of sides at the verge of the Icosahedron is 3.

• The number of edges adjacent at the top of the Icosahedron is 5.

### Surface Area of Icosahedron

Let ‘a’ be the length of the sides of the icosahedron, then the  surface area of the icosahedron is calculated by using the following formula:

Surface Area of Icosahedron Formula =  $5\sqrt{3}\times a^{2}$

### Volume of Icosahedron

Let ‘a’ be the length of the sides of the icosahedron, then the volume of the icosahedron is calculated by using the following formula:

Volume of Icosahedron Formula =  $\frac{5}{12}\times (3+\sqrt{5})\times a^{3}$

### What is an Icosahedron Shape Used For?

n magic 8 balls, answers are inscribed in regular icosahedron shape.

Icosahedron shape is widely used in card games, board games, and even in video games.

An icosahedron is a three-dimensional board game for icosagame, formerly known as the Ico Crystal Game.

A world map was defined in the form of an unfolded icosahedron by R. Buckminster Fuller, and Japanese cartographer Shoji Sadao, known as fuller projection, whose maximum distortion is only 2 %.

The logo of the American Electronic music duo ODESZA used a regular icosahedron.

### Solved Example

1. What is the Volume of the Face Dice Shape Looks Like an Icosahedron With a Side Length of 5 in.

Solution:

Length of the side of the face dice shape looks like an Icosahedron =  5 in

Volume of Icosahedron =  $\frac{5}{12}\times (3+\sqrt{5})\times a^{3}$

Volume =  $\frac{5}{12}\times (3+\sqrt{5})\times 5^{3}$

=  $\frac{625}{12}\times (3+\sqrt{5})\times 5^{3}$

= $\frac{625}{12}\times (3+\sqrt{5})$

= 272,71 cm3

Therefore, the volume of the icosahedron is 272,71 cm3.

2. What is the Surface Area of Icosahedron Whose Volume is 139.628 in3 and the Length of the Side is 4 in?

Solution:

As we know,

Volume of Icosahedron =  $\frac{5}{12}\times (3+\sqrt{5})\times a^{3}$

Surface Area of Icosahedron = $5\sqrt{3}\times a^{2}$

On dividing the surface area of icosahedron by volume of the icosahedron, we get:

$\frac{Area}{Volume}=\frac{4}{a}$

$A=\frac{V\times a}{4}$

$A=\frac{139.628\times 4}{4}$

A = 139,628 in2

Therefore, the surface area of Icosahedron is 139,628 in2.

1. What is Truncated Icosahedron?

Ans: In Geometry, truncated icosahedron is an American solid, one of the 13 convex isogonal non-prismatic solid, whose 32 faces are two or more than two types of a regular polygon.

Truncated Icosahedron consists of 12 regular pentagonal faces, 20 regular hexagonal faces, 60 vertices, and 90 edges. The truncated icosahedron shape is used in constructing soccer balls where black pentagons and white hexagons are joined together.

2. What is the Difference Between Icosahedron and Dodecahedron?

Ans: The difference between Icosahedron and Dodecahedron are as follows:

 Icosahedron Dodecahedron Number of Vertices 12 20 Number of Edges 30 30 Number of Faces 20 12 Volume/Length 2.182 7.663 Symbolizes Water Universe

3. Who Discovered Regular Icosahedron Shape?

Ans: The regular Icosahedron shape is discovered by Athenian mathematician Theatetus (c. 417–369 BC) along with Octahedron. Icosahedron and Octahedron were discovered by Theateus while the other three platonic solids were discovered by Plato.