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Geometry Level 4

There Is A Right Triangle Whose Hypoteneuse(Longest Side Or The Side Opposite To The Right Angle)

Is Of Length 20 units . Find The Sum Of Squares Of Lengths Of Medians Of The Triangle.

Details And Assumptions

  1. Median Is A Line Segment From Any Vertex Of The Triangle Which Has Its Other End Point As

    The Midpoint Of Opposite Side .

  2. Sum Of Square Of Lengths Means If You Get 3,4,5 as the answer

    then enter the answer as 3^2+4^2+5^2 = 50

3.If You Think Data Is Insufficient Then Enter The Answer As Zero (0).


The answer is 600.

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2 solutions

Prakhar Bindal
Oct 19, 2015

Today In The Morning I Was Looking At The Derivation Of The Formula Of Length Of Medians Of A

Triangle. Then I Noticed That If We Wish To Find The Sum Of Squares Of Medians We Can Get A Nice

Result = 3/4(a^2+b^2+c^2) . Then On Further Observation I Observed That For A Right Triangle The

Result Can Be Simplified To 3/2(c^2) by using the pythagorean identity . Where c is length of longest side)

Well I Dont Know That This Observation Was Made Earlier Or Not By Anyone(But I Think It Would Have

Been Made Because It Is Not A Great Thing To Observe) :P

Well The Result Can Be Derived Easily Using Apollonius Theorem .

In A Triangle ABC Where AD Is the median

Even I did it by the same concept !!

Akshat Sharda - 5 years, 7 months ago

I TOOK THE SIDES 20, 16, 12: WHICH MADE MY CALCULATIONS SIMPLER

Anubhav Tyagi - 4 years, 12 months ago

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I did the same, and assumed that the answer must either be this or 0 (That not enough information was provided) Since I had 3 guesses, I knew I was good! ;-)

Geoff Pilling - 4 years, 3 months ago

It wont be simpler than this . just 3/2 * 400 = 600! . Provided you know apollonius theorem of course

Prakhar Bindal - 4 years, 3 months ago

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i used 10root3 , 10 , 20

A Former Brilliant Member - 4 years, 1 month ago
Gopal Narayanan
Nov 8, 2015

Use coordinate geometry. Median 1 length is a^2 +b^2/4. Median 2 is b2+a2/4. Median 3 is a2/4+b2/4

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