# CBSE Class 6 Maths Revision Notes Chapter 4

## CBSE Class 6 Mathematics Chapter 4 Revision Notes – Basic Geometrical Ideas

Extramarks brings to you Class 6 Mathematics Chapter 4 Notes to develop an in-depth understanding of the basic geometrical ideas. The experts have made sure that all the concepts given in the NCERT Mathematics book are covered in these notes. With these notes, students will be able to revise the entire chapter quickly and effectively.

## Revision Notes CBSE Class 6 Mathematics Chapter 4

### Access Class 6 Mathematics Chapter 4 – Basic Geometrical Ideas Notes PDF

An Introduction To Basic Geometrical Ideas

The chapter named Basic Geometrical Ideas introduces students to basic geometrical ideas which are crucial for understanding geometry at a later stage. Class 6 Mathematics Chapter 4 Notes help students develop a solid foundation in geometry so they do not face any difficulty while dealing with geometrical figures. The notes comprise the following topics.

• Point
• Line Segment
• Line
• Parallel Lines
• Intersecting Lines
• Ray
• Angle
• Curve
• Polygon
• Triangle
• Circle

Geometrical Terms: Basic Definitions

Point

• In geometry, a point is a dot that represents a location. It does not have any length, breadth, or height. In other words, it has no dimension. It is usually represented by capital letters.

Line Segment

• When two points are joined by a straight line, that straight line is called a line segment.
• A line segment is the shortest distance between two points.

Line

• When a line segment is extended on both sides to infinity, it is called a line.
• Sometimes, a line is represented by a small “l”.

Parallel Lines

• When two lines are extended and they do not cross each other, then these two lines are called parallel lines.
• Parallel lines never cross each other, even if they are extended up to an infinite.

Intersecting Lines

• It is like the opposite of parallel lines. When two lines cross each other after extending them and meet at a point, these lines are called intersecting lines.
• The meeting point is called the point of intersection.
• Ray
• A ray is a segment of a line that has a beginning point but no endpoint.
• Ray starts with a particular point and extends up to the infinite.
• A ray extends  in one direction only.

Angle

• An angle is a geometrical figure formed by two intersecting rays.
• These rays are also called arms.
• The common endpoint, or the intersecting point, is called the vertex.
• An angle divides the surface into three sections or regions, such as, on the angle, inside the angle, and outside the angle.

Curve

• A curve is a drawing that starts from a particular point and moves in any direction without any break in between.
• In that sense, a straight line and a circle are both curves.
• A straight line is called a simple curve as it does not cross itself.
• If the endpoints of a curve meet each other, the curve is called a closed curve.
• If the endpoints do not meet, the curve is called an open curve.

Polygons

• A polygon is a closed curve.
• The sides of a polygon are made of line segments.
• These line segments are called edges.
• The meeting point of the two edges is called the vertex.
• At every vertex, there is an angle.
• The two edges of a polygon that share a common vertex are called the adjacent sides.
• A straight line that joins two non-adjacent vertices is called a diagonal.
• Polygonal shapes include triangles, rectangles, squares, octagons, and others.

• When a polygon is formed by four rays, it is called a quadrilateral.
• It has two pairs of opposite edges.
• It has two pairs of opposite angles.
• Every angle has two adjacent angles.

Triangle

• A triangle is also a polygon that has three sides.
• A triangle has three angles.

Circle

• When the starting point and the meeting point of a curve are the same, the curve is called a circle.
• A fixed point situated inside a circle from which the distance of every point located on the circle is equal is called the center of the circle.
• The distance between the center and any point located on the circle is called the radius of the circle.
• A chord is a line segment that joins any two points located on the circle.
• The diameter is a chord that passes through the center.
• Thus, a diameter cuts the circle into two equal halves. Each half is called a semi-circle.
• An arc is a segment of the circle that has two endpoints.
• A chord is located inside the circle; an arc is situated on the circle.
• The area enclosed by an arc and a pair of radii is called a sector.
• When an area inside the circle is enclosed by an arc and a chord, it is called the circle segment.

### 1. What are the intersecting lines?

When two lines cross each other, they are called intersecting lines.

### 2. What are parallel lines?

When two lines run smoothly without crossing each other, they are called parallel lines.

### 3. What is a circle?

A circle is a round geometrical figure that contains radii of the same length.

### 4. Is a quadrilateral a polygon?

A polygon can have a number of edges. A quadrilateral is a special type of polygon that is formed by four edges.

### 5. What is the difference between a sector and a circle segment?

A sector is formed by an arc and two radii of a circle, whereas a circle segment is formed by an arc and a chord of the circle.

### 6. What is the length of a diameter?

The length of a diameter is twice the length of the radius of the same circle.

### 7. How many points are required to draw a straight line?

Only two points are required to form one line.

### 8. What is the minimum number of points required to draw a circle?

Only one point is enough to draw a circle.

### 9. What is the name of the geometrical figure that has three edges?

The geometrical figure that has three edges is called a triangle.