Geometry

Triangle, circle, and quadrilateral angle properties — the most frequently repeated theorems in RRB geometry questions.

📖 ~4 min read 📐 RRB NTPC / Group D — Mathematics

Topic	Rule
Angle sum of a triangle	Sum of all three angles = 180°
Exterior angle theorem	Exterior angle = sum of the two opposite interior angles
Pythagoras theorem	Hypotenuse² = Base² + Height² (right triangle only)
Angle sum of a quadrilateral	Sum of all four angles = 360°
Angle in a semicircle	Always 90°
Tangent-radius property	A tangent is always perpendicular to the radius at the point of contact

💡 Pythagorean triples to memorise: 3-4-5 | 5-12-13 | 8-15-17 | 7-24-25 | 9-40-41 (and their multiples)

💡 Example: Right triangle with base 6, height 8 → Hypotenuse² = 36+64 = 100 → Hypotenuse = 10

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