Class 6 Maths Chapter 2 Lines and Angles Revision Notes

Quick revision notes for Class 6 Maths Chapter 2, “Lines and Angles” — all key definitions and facts at a glance for fast last-minute review. These Class 6 Mathematics Chapter 2 notes are ideal for quick revision just before exams.

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.

Written by Satish

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