What You’ll Learn

In this chapter, you will understand:

• Basic concepts of geometry like points, lines, and shapes

• Different types of lines and angles

• Parts of geometrical figures like triangles, circles, quadrilaterals, etc.

• Names and properties of these shapes

  Key Concepts

  1. Point

  • A point shows an exact location.

  • It has no size, length, or breadth.

  • Represented by a dot and usually named using capital letters like A, B, C.

    Example:
    Point A

    2. Line, Line Segment, and Ray

    Concept	Definition	Representation
    Line	A straight path that extends endlessly in both directions	↔ AB
    Line Segment	A part of a line with two fixed endpoints	─ AB
    Ray	A part of a line that starts at one point and goes endlessly in one direction	→ AB

    3. Intersecting and Parallel Lines

    • Intersecting Lines: Two lines that meet at a point.

    • Parallel Lines: Lines that never meet, no matter how far they are extended

      Example:
      Train tracks are parallel lines.

      4. Curves and Polygons

      • Curve: Any continuous and smooth flowing line without sharp angles.

      • Simple Curve: Does not cross itself.

      • Closed Curve: Starts and ends at the same point.

      Polygon: A closed figure made up of straight lines (sides).

      Examples of polygons:

      • Triangle (3 sides)

      • Quadrilateral (4 sides)

      • Pentagon (5 sides)

      • Hexagon (6 sides)

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      5. Angles

      • Formed when two rays meet at a common point (called vertex).

      • Represented as ∠ABC (with B as the vertex).

      Types of angles (introduced later but can be mentioned):

      • Acute (< 90°)

      • Right (= 90°)

      • Obtuse (> 90° and < 180°)

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      6. Triangles

      • A polygon with 3 sides and 3 angles.

      • Types (based on sides and angles) introduced in later classes.

      Parts:

      • Sides

      • Vertices

      • Angles

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      7. Quadrilaterals

      • A polygon with 4 sides and 4 angles.

      • Examples: square, rectangle, rhombus, trapezium

      Parts:

      • Sides

      • Vertices

      • Diagonals (line joining opposite corners)

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      8. Circles

      • A closed curve where every point is equidistant from a fixed point (centre).

      Parts of a circle:

      • Centre – the fixed point

      • Radius – distance from centre to any point on the circle

      • Diameter – line passing through centre joining two points on the circle (twice the radius)

      • Chord – a line joining any two points on the circle

      • Arc – part of the circle

      • Sector – region between two radii and the arc

      • Segment – region between a chord and the arc