Apply Ceva's Theorem, I Don't Think

Geometry Level 5

Let there be a triangle A B C ABC with A D AD being a line passing through A A intersecting B C BC (not extended) at D D and B E BE being the line passing through B B and intersecting A C AC (not extended) at E E let the intersection of A D AD and B E BE be H H .

If the area of Δ A H E \Delta AHE be 2 2 , the area of Δ A H B \Delta AHB be 3 3 and the area of Δ B H D \Delta BHD be 4 4 . Find the area of C D H E CDHE .


The answer is 96.

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2 solutions

Sharky Kesa
Mar 31, 2016

I will write a general solution for when the area of Δ A H E \Delta AHE is a a , the area of Δ A H B \Delta AHB is b b and the area of Δ B H D \Delta BHD is c c .

Note that triangles on collinear bases with equal altitudes have their areas proportional to the lengths of their bases.

By this above property, we have that E H H B = a b \dfrac{EH}{HB} = \dfrac{a}{b} and A H H D = b c \dfrac {AH}{HD} = \dfrac {b}{c} . Draw line C H CH and let the areas of Δ C H E \Delta CHE and Δ C H D \Delta CHD be d d and e e respectively. Notice that Δ C A H \Delta CAH and C H D CHD have collinear bases and have equal altitude. Thus, B H H E = a + e d \dfrac {BH}{HE} = \dfrac {a+e}{d} . Similarly, A H H D = d c + e \dfrac {AH}{HD} = \dfrac {d}{c+e} . Thus, we have the following:

b c = d c + e a b = a + e d \begin{aligned} \dfrac {b}{c} &= \dfrac {d}{c+e}\\ \dfrac {a}{b} &= \dfrac {a+e}{d} \end{aligned}

Solving the simultaneous linear equations in terms of d d and e e , we get d = a c ( a + b ) b 2 a c d=\dfrac {ac(a+b)}{b^2-ac} and e = a c ( b + c ) b 2 a c e=\dfrac {ac(b+c)}{b^2-ac} , so the area of C D H E = d + e = a c ( a + 2 b + c ) b 2 a c CDHE=d+e=\dfrac {ac(a+2b+c)}{b^2-ac} . Substituting the values from the question is, we get the answer of 96. Thus, the answer is 96.

i have solved in the same way.

Niranjan Khanderia - 5 years, 2 months ago

Do you mean that point "H" instead of point "F" ?.

Please, do that in your problem as a correction.

Ahmad Saad - 5 years, 2 months ago

Isn't H = F H=F ? Great problem though!

A Former Brilliant Member - 5 years, 2 months ago

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Yeah, sorry, I typoed. Thanks!

Sharky Kesa - 5 years, 2 months ago

Confused how did X suddenly come ??????

vishwash kumar - 4 years, 7 months ago

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Sorry, typo! Fixed.

Sharky Kesa - 4 years, 7 months ago
Prayas Rautray
Sep 27, 2017

I will use the property that in the given quadrilateral [ A E H ] [ B H D ] = [ E H D ] [ A H B ] [∆AEH][∆BHD]=[∆EHD][∆AHB]
Where [∆ABC] denotes Area of ∆ABC.
Plugging in the values, we get [ E H D ] = 8 3 [∆EHD]=\frac {8}{3} .
Note that triangles on collinear bases with equal altitudes have their areas proportional to the lengths of their bases, as stated by SHARKY sir. So, C D D B = [ E D C ] [ E D B ] = [ A C D ] [ A D B ] \frac {CD}{DB}= \frac {[∆EDC]}{[∆EDB]} = \frac {[∆ACD]}{[∆ADB]} .
Again plugging in the values we get area of ∆ECD=93.33. So area of CEHD= 96



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