CBSE Class 6 Maths — Basic Geometrical Ideas

Points, Lines and Line Segments

Geometry starts with basics!

1. Point: A point determines a location. It has no length, width, or depth (thickness). Usually denoted by a capital letter like A, B, or P.

2. Line Segment: The shortest straight path between two points. It has a fixed length. Denoted as $\overline{AB}$.

  A -------------------- B
 (Start)                (End)

3. Line: A line segment extended indefinitely in both directions. A line containing points A and B is denoted as $\overleftrightarrow{AB}$. It has no fixed length.

<------------------------>

4. Intersecting Lines: Two distinct lines meeting at a single point (point of intersection). Like the letter ‘X’.

5. Parallel Lines: Lines on a plane that never meet, no matter how far they are extended. Like railway tracks. Denoted as $l \parallel m$.

6. Ray: A portion of a line that starts at one point (starting point) and goes endlessly in a particular direction. Like a sunbeam. Denoted by $\overrightarrow{OP}$.

  O -------------------->

Curves and Polygons

Curves: Drawings done without lifting the pencil from the paper.

• Open Curve: The starting point and end point are different.
• Closed Curve: The starting point and end point meet.

Polygons: A closed figure made up entirely of line segments.

• Vertices: The corners where sides meet.
• Diagonals: The line segments joining two non-adjacent vertices.

Angles

An angle is formed when two rays originate from the same endpoint.

• The two rays forming the angle are its arms.
• The common endpoint is the vertex.
• An angle separates the plane into the interior (inside) and the exterior (outside).

Circles

A closed curve consisting of all points at a fixed distance from a central point.

graph TD
    Circle --> Center["Center (O)"]
    Circle --> Radius["Radius (R): Center to edge"]
    Circle --> Diameter["Diameter (D = 2R): Edge to edge passing through center"]
    Circle --> Chord["Chord: Line connecting two points on edge"]
    Circle --> Arc["Arc: A portion of the circumference"]
    Sector["Sector: Area enclosed by 2 radii and an arc like a pizza slice"]
    Segment["Segment: Area enclosed by a chord and an arc"]
    Circle -.-> Sector
    Circle -.-> Segment