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In fig triangle ABC is an …

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In fig triangle ABC is an equilateral triangle in which AD is perpendicular to BC prove that 3AD×AD = 4AD×AD
  • 1 answers

Sia ? 6 years, 4 months ago


In equilateral {tex}\Delta ABC{/tex}, AD{tex}\perp{/tex}BC
and AB=BC=CA 
Also BD={tex}\frac{BC}{2}{/tex}.....(1)
So, {tex}\Delta ABD{/tex} is right-angled triangle
By the Pythagoras theorem,
AB= AD+ BD2
{tex}\Rightarrow{/tex} AB= AD+ ({tex}\frac{BC}{2}{/tex})2
{tex}\Rightarrow{/tex} AB= AD{tex}\frac{BC^2}{4}{/tex}
{tex}\Rightarrow{/tex} 4AB= 4AD+ BC2
{tex}\Rightarrow{/tex} 4AB= 4AD+ AB2 (AB = BC)
{tex}\Rightarrow{/tex} 4AB= 4AD+ AB2 
{tex}\Rightarrow{/tex} 4AB- AB= 4AD2
{tex}\Rightarrow{/tex} 3AB= 4AD2
Hence Proved.

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