 # Geometry

Geometry is derived from two Greek words, geo + metron, meaning earth & measurement. Thus it is concerned with the properties and relations of points, lines, surfaces, solids, and higher dimensional analogues. We study geometry to find the Length, Area, Volume of different Plane and Solid figures which are present around us in this world and to know better about them. Knowledge of coordinate geometry provides many fundamental skills and helps us to improve problem-solving skill, logical skill, analytical reasoning skill and so on. Here, you are going to have a look at the basics of Geometry, its branches, plane geometry as well as solid geometry in detail.

## Branches of Geometry (i) Algebraic Geometry – is a branch of geometry studying zeros of the multivariate polynomial. It includes linear and polynomial algebraic equations that are used for solving the sets of zeros. The application of this type comprises Cryptography, string theory, etc.

(ii) Discrete Geometry – is concerned with the relative position of simple geometric object, such as points, lines, triangles, circles etc.

(iii) Differential Geometry – uses techniques of algebra and calculus for problem-solving. The various problems include general relativity in physics etc.

(iv) Euclidean Geometry – The study of plane and solid figures based on axioms and theorems including points, lines, planes, angles, congruence, similarity, solid figures. It has a wide range of applications in Computer Science, Modern Mathematics problem solving, Crystallography etc.

(v) Convex Geometry – includes convex shapes in Euclidean space using techniques of real analysis. It has application in optimization and functional analysis in number theory.

(vi) Topology – is concerned with properties of space under continuous mapping. Its application includes consideration of compactness, completeness, continuity, filters, function spaces, grills, clusters and bunches, hyperspace topologies, initial and final structures, metric spaces, nets, proximal continuity, proximity spaces, separation axioms, and uniform spaces.

## Geometry Formulas

To calculate the area, perimeter, volume and different measures using length, breadth and height of different geometrical figures, geometry formulas are important. By using the formulas, we can calculate the measures easily. There are loads of formulas to learn in Geometry. Here, you are provided with all the important geometry formulas in the PDF. Download the below-given PDF to learn and solve all the problems related to geometry.

## Plane Geometry

Plane Geometry deals with flat shapes which can be drawn on a piece of paper. These include lines, circles & triangles of two dimensions. Plane geometry is also known as a two-dimensional geometry. All the two-dimensional figures have only two measures such as length and breadth. It does not deal with the depth of the shapes. Some examples of plane figures are square, triangle, rectangle, circle, and so on. Here, some of the important terminologies in plane geometry are explained.

### Point

A point is a precise location or place on a plane. A dot usually represents them. It is important to understand that a point is not a thing, but a place. Also, note that a point has no dimension; preferably, it has the only position.

### Line

The line is straight (no curves), having no thickness and extends in both directions without end (infinitely). It is important to note that it is the combination of infinite points together to form a line. In geometry, we have a horizontal line and vertical line which are x-axis and y-axis respectively. • Line Segment – If a line has a starting and an endpoint then it is called a Line Segment.
• Ray – If a line has a starting point and has no endpoint is called Ray.

Eg. Sun Rays

### Angles

In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.

Types of Angle

Acute Angle – An Acute angle (or Sharp angle) is an angle smaller than a right angle ie. it can range between 0 – 90 degrees.

Obtuse Angle – An Obtuse angle is more than 90 degrees but is less than 180 degrees.

Right Angle – An angle of 90 degrees.

Straight Angle – An angle of 180 degrees is a straight angle, i.e. the angle formed by a straight line ### Polygon

A plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed polygonal chain or circuit.

The name ‘poly’ refers to multiple. An n-gon is a polygon with n sides; for example, a triangle is a 3-gon polygon.

General Formula for Sum of internal Angles of a polygon –

Sum of internal Angles of a polygon = $(n-2)\times 180$

Types of Polygon Polygon type Definition & Property Types (i) Triangle – A 3-sided polygon whose sum of internal angles always sums to 180 degrees. Equilateral Triangle – Has 3 equal sides and angles. Isosceles triangle –  Has 2 equal sides and angles. Scalene triangle – Has all the 3 unequal sides and angles. (ii) Quadrilateral A 4-sided polygon with four edges and four vertices. Sum of internal angles is 360 degrees Square – Has 4 equal sides and vertices which are at right angles. Rectangle – Has equal opposite sides and all angles are at right angles. Parallelogram – has two pairs of parallel sides. The opposite sides & opposite angles are equal in measure. Rhombus – Has all the four sides to be of equal length. However, they do not have its internal angle to be 90 degrees Trapezium – Has one pair of opposite sides to be parallel. (iii) Pentagon A plane figure with five straight sides and five angles (iv) Hexagon A plane figure with six straight sides and six angles (v) Heptagon A plane figure with seven sides and seven angles (vi) Octagon A plane figure with eight straight sides and eight angles. (vii) Nonagon A plane figure with nine straight sides and nine angles. (viii) Decagon A plane figure with ten straight sides and ten angles.

### Circle

A Circle is a simple closed shape. From a certain point called the centre, all points of a circle are of same consistent distance, i.e. the curve traced out by a point that moves so that its distance from the centre is constant. #### Understanding Similarity and Congruence

Similarity – Two figures are said to be similar if they have the same shape or have an equal angle but do not have the same size.

Congruence –  Two figures are said to be Congruent if they have the same shape and size. Thus, they are totally equal.

## Solid Geometry

Solid Geometry deals with 3-dimensional objects like cubes, prisms, cylinders & spheres. It deals with three-dimensions of the figure such as length, breadth and height. But some solid solids do not have faces (e.g. sphere).  It is the study of three dimensions in the Euclidean space. The objects which are around us are three-dimensional. All the three-dimensional shapes are obtained from the rotation operation of 2D shapes. The important attributes of 3D shapes are faces, edges, and vertices. Go through with these terms in detail for different geometric shapes here.

### Edges

An edge is defined as the line segment on the boundary that joins one vertex to the other vertex. It means that it joins one corner point to the other. It forms the skeleton of 3D shapes.  In other words, it can be defined as the faces, that meets in the straight line is called edge. Following are the list of edges for the different solid shapes:

 Solid Shapes No. of. Edges Triangular Prism 9 Cube 12 Rectangular prism 12 Pentagonal Prism 15 Hexagonal Prism 18 Triangular Pyramid 6 Square Pyramid 8 Pentagonal Pyramid 10 Hexagonal Pyramid 12

### Faces

We know that all the geometric shapes are made up of flat surface called faces. It is a flat surface enclosed by the edges. For any three-dimensional shapes, the face should be a two-dimensional figure. The list of the number of faces for different solid shapes are given below:

 Solid Shapes No. of. Faces Triangular Prism 5 Cube 6 Rectangular prism 6 Pentagonal Prism 7 Hexagonal Prism 8 Triangular Pyramid 4 Square Pyramid 5 Pentagonal Pyramid 6 Hexagonal Pyramid 7

### Vertices

A vertex is defined as the point where the edges of the solid figure meet at each other. In other words, it can be said that, the point where the adjacent sides of the polygon meet. The vertex is the corners where the edges meet. The number of vertices for different solid shapes in  geometry is as follows:

 Solid Shapes No. of. Vertices Triangular Prism 6 Cube 8 Rectangular prism 8 Pentagonal Prism 10 Hexagonal Prism 12 Triangular Pyramid 4 Square Pyramid 5 Pentagonal Pyramid 6 Hexagonal Pyramid 7

## Frequently Asked Questions of Geometry

### How geometry is used?

Geometry is used in configuring and measurement of different shapes and sizes, such as circles, squares, cubes, triangles, etc.

### What are all the Geometry applications?

Geometry has wide usage in daily life. Its major applications are in the field of constructions, such as the construction of building, roads, dams, bridges, etc. and also in surveying, mapping, navigation. In software industries, it is used in graphics designing, gaming, animations, etc. In the medical field as well, for CT scanning and MRI’s geometry concepts are used.

### Why geometry is important?

In our lives, geometry is important to understand the various shapes and measure them based on area and volumes.

### What geometry means?

Geometry means the measurement of Earth, as it derived from the ancient Greek words, ‘geo’ means Earth and ‘metron’ means measurement. So any object which is present on earth has a shape which is defined by geometry.

#### 1 Comment

1. Sai Nirjara Pani

It is a nice app to learn