A geometry problem by Pranay Kr

Geometry Level 4

In a A B C \triangle ABC , A B = 13 AB=13 , B C = 15 BC=15 , and C A = 17 CA=17 . Point D D is on line A B AB , E E is on line B C BC , and F F is on line C A CA . Let A D = p × B E = q × B C AD=p \times BE=q \times BC , and C F = r × C A CF=r \times CA , where p p , q q , and r r are positive and satisfy p + q + r = 2 3 p+q+r=\dfrac 23 and p 2 + q 2 + r 2 = 2 5 p^2+q^2+r^2= \dfrac 25 . The ratio of the area of D E F \triangle DEF to the area of A B C \triangle ABC can be written in the form m n \dfrac mn , where m m and n n are relatively prime positive integers. Find m + n m+n .


The answer is 61.

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1 solution

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Oct 10, 2017

The key is to consider [AFD] [EFC] {BED]

[AFD]/[ABC]=AD(AF)/(AB)(AC) = p(1-r)

proceed similar for others and answer comes immediate

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