Basic Geometrical Ideas Class 6 Notes: Chapter 4

Basic geometrical ideas class 6 notes covers all the important concepts included in this chapter along with examples and practice questions. These CBSE class 6 chapter 4 notes will not only help the students to learn the concepts more easily but will also help them to revise this chapter more effectively.

Introduction to Basic Geometrical Ideas

In this chapter, several important geometric terms are included which holds extreme importance in the later grades. The topics that are introduced not only will help students to build a foundation in geometry but will also help them to grasp the higher level concepts in the later grades easily.

The main topics covered here are-

  • Basic Definitions in Geometry
  • Polygons
  • Triangles
  • Quadrilaterals
  • About Circles

Basic Definitions in Geometry

Terms Definition
Point It determines a location and is usually determined by a capital letter.
Line segment The shortest distance between two points is called a line segment.
Line By extending a line segment indefinitely on both sides, a line is obtained.
Intersecting lines If two distinct lines meet or cross at a point, they are called intersecting lines.
Parallel lines Parallel lines are lines which are always the same distance apart and never intersect anywhere in a plane.
Ray A ray is a line which starts from a particular point and goes infinitely towards a particular direction.
Curve It is a drawing which is done without lifting the pencil.
Simple curve A curve that never crosses itself is a simple curve.
Closed and open curves A curve is closed if its ends are joined. Otherwise, it is a open curve.
Angle It is made up of two rays which are starting from a common point.


A polygon can be defined as a closed curve which is made up of line segments. Polygons can be of numerous types like triangles (having 3 line segments), quadrilaterals (having 4 line segments), pentagon (having 5 line segments), and so on. A few important terms related to polygons are-

Terms Definition
Sides of a polygon The line segments are known as the sides of the polygon.
Adjacent sides Two points having the same endpoint are called adjacent sides.
Vertex Vertex is the meeting or intersecting point of a pair of sides.
Diagonal Diagonal is obtained by joining any two non-adjacent vertices of a polygon.


A triangle is as a polygon having three line segments or sides. A triangle ABC is written as \(\triangle ABC\) as given below-

Basic Geometrical Ideas Class 6 Notes: Chapter 4

In this triangle, AB, BC, and AC are sides of the triangle and A, B, C are the vertices of the triangle. Also, the angle between BC and AB is the \(\angle B\), between BC and AC, it is \(\angle C\), and between AB and AC, it is \(\angle A\).


A quadrilateral is defined as a four-sided polygon i.e. having 4 line segments or sides and thus, 4 angles. A diagram of a quadrilateral is given for better understanding. It should be noted that the vertices of a quadrilateral are named in a cyclic manner.

Basic Geometrical Ideas Class 6 Notes: Chapter 4

In this diagram, AD and DC are one of the examples of adjacent sides. Also, AD and BC are one of the opposite sides. Here, angle A and angle C are opposite angles. In this, if line segment is drawn from A to C or from B to D, it becomes a diagonal.

About Circles

A circle can be defined as a closed figure formed by a set of points in a plane which are located at the same distance from a fixed point which is the center. A few important terms related to circles are-

Terms Definitions
Radius The fixed distance at which the points are located from the center is called the radius.
Diameter Diameter is the length of a line segment which joins any two points on the circle by passing through the center. Diameter is always double than the radius.
Circumference The distance around the circle is known as its circumference or perimeter.
Chord A line segment joining any two points on the circle is a chord.
Sector It is the region in the interior of a circle which is enclosed by an arc on one side and a pair of radii on the other two sides.
Segment It is a region in the interior of the circle enclosed by an arc and a chord.

Practice Questions

  1. Draw a quadrilateral ABCD and state its pair of opposite sides and angles, and pair of adjacent sides and angles.
  2. Is having a polygon of two sides possible? Illustrate.
  3. Two diameters of a circle will always intersect. Justify.

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Practise This Question

Which one of the following lies between 0.3 and 0.7?