Class 6 Maths Chapter 2 Lines and Angles Revision Notes

Chapter 2 opens with the basic building blocks of geometry — points, lines, rays, and segments — before moving into how angles are classified and measured, all summarised here for a fast recap.

Last Updated: September 23, 2026

Basic Geometric Terms

• Point: a location; no length, width, or size.
• Line segment: shortest path between two fixed endpoints; has a definite length. Written as segment AB = segment BA.
• Line: extends endlessly in both directions through two points; no fixed length. Written as line AB = line BA.
• Ray: starts at one fixed endpoint and extends endlessly in one direction only. Written as ray OA (O = starting point, always named first). Ray OA ≠ ray AO. A ray can be renamed using any other point that lies on it (ray OA = ray OB if B also lies on the same ray from O).

Angles: Definition and Naming

• An angle forms where two rays (the arms) share a common starting point (the vertex).
• Named with 3 letters, vertex in the middle: angle APB = angle BPA.
• If multiple angles share one vertex, you must use all 3 letters — “angle P” alone would be ambiguous.

Types of Angles (Quick Table)

• Right angle = half of a straight angle (90° = 180° ÷ 2).
• Sum of angles in any triangle = 180° (always).

Clock Hand Angles (Formula)

Each hour mark = 360° ÷ 12 = 30° apart. Smaller angle between hands = smaller of (hour × 30°) and (360° − hour × 30°).

Key Solved Facts

• Pattern 3, 12, 21, … → +9 each time (arithmetic) → next term = 30.
• Ashoka Chakra: 24 spokes → 15° between adjacent spokes; largest acute angle = 75° (5 gaps of 15°).
• Acute-angle puzzle: 4x acute and 5x obtuse → x ∈ {19°, 20°, 21°, 22°}.
• 3 non-collinear points → 3 lines, 3 angles. 4 points (no 3 collinear) → 6 lines, 12 angles.
• Angles are compared by superimposition (tracing paper) and measured precisely with a protractor, in degrees.

Quick revision: Solutions | Extra Questions for this chapter.

Frequently Asked Questions

What is the difference between a line, a line segment, and a ray?
A line extends infinitely in both directions with no endpoints, a line segment has two fixed endpoints and a definite length, and a ray has one fixed starting point but extends infinitely in only one direction.

How are angles classified based on their measure?
Angles are classified as acute if less than 90 degrees, right if exactly 90 degrees, obtuse if between 90 and 180 degrees, straight if exactly 180 degrees, and reflex if between 180 and 360 degrees.

Written by Satish

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