Ex 6.5, 16 - Prove that three times the square of one side - Ex 6.5

  1. Chapter 6 Class 10 Triangles
  2. Serial order wise
Ask Download


Ex 6.5, 16 In an equilateral triangle, prove that three times the square of one side is equal to four times the square of one of its altitudes. Given:- Equilateral triangle ABC with each side a & AD as one of its altitudes To Prove :- 3 × Square of one side = 4 × square of one of it’s altitude ⇒ 3a2 = 4AD2 Proof:- In Δ ADB & Δ ADC AB = AC AD = AD ∠ ADB=∠ ADC Hence ∆ ADB ≅ ∆ ADC Hence , BD = DC BD = DC = 1/2BC BD = DC = 𝑎/2 Now, ADB is a right angle triangle Using Pythagoras theorem (Hypotenuse)2 = (Height)2 + (Base)2 (AB)2 = (AD)2 + (BD)2 (a)2 = AD2 + (1/2 𝑎)2 a2 = AD2 + 𝑎2/4 a2 – 𝑎2/4=𝐴𝐷2 (4𝑎2 − 𝑎2)/4=𝐴𝐷2 3𝑎2/4=𝐴𝐷2 3a2 = 4 ×𝐴𝐷2 3a2 = 4AD2 Hence proved

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 7 years. He provides courses for Mathematics and Science from Class 6 to 12. You can learn personally from here https://www.teachoo.com/premium/maths-and-science-classes/.
  • Badal Verma's image
    prove that in a triangle if the square of one side is equal to the sum of the squares of the other two sides the angle of opposite to the first side is a right angle using the Converse of above determine the length of an altitude of an equilateral triangle of Side 2 centimetre
    View answer