Class 7 · Chapter 7
A Tale of Three Intersecting Lines
Triangles: properties, angle sum, exterior angle.
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Ganita Prakash · Class 7 Part 1 (2026-27)
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Detailed theory
All three interior angles add to . In an equilateral, each is .
Key concepts & formulas
01
A triangle has 3 sides, 3 vertices, 3 angles.
02
**Angle sum** = .
03
**Exterior angle** = sum of two remote interior angles.
04
Types: scalene, isosceles, equilateral (by sides); acute, right, obtuse (by angles).
05
Triangle inequality: sum of any two sides > third.