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CBSE Class 10 Mathematics Question 66 of 78

Triangles — Question Ex 6.5 Q15

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Ex 6.5 Q15
Question

In an equilateral triangle ABC, D is a point on side BC, such that BD = \(\frac { 1 }{ 3 }\)BC. Prove that 9AD2 = 7AB2.

Answer

Ch 6 Maths Class 10 Ex 6.5 NCERT Solutions PDF Q15

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CBSE Class 10 Triangles — Complete Guide

Triangles carries the highest marks in Geometry (8-10 marks). BPT proof and Pythagoras theorem proof are must-prepare topics.

Quick Revision: Key Concepts

  • BPT: If DE ∥ BC, then AD/DB = AE/EC
  • Similarity criteria: AA, SSS, SAS
  • Area ratio: ar(▵1)/ar(▵2) = (side ratio)²
  • Pythagoras: hypotenuse² = base² + perpendicular²

Most Important Questions

  1. Prove BPT (Thales' theorem) — 5 marks guaranteed
  2. Prove Pythagoras theorem using similarity
  3. Prove triangles are similar using AA/SSS/SAS and find unknown sides
  4. Area ratio problems

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