A geometry problem by Soumava Pal

Geometry Level 3

A triangle with vertices A , B , C A,B,C with coordinates ( 2 , 1 2 ) \left(2,\frac{1}{2}\right) , ( 4 , 1 4 ) \left(4,\frac{1}{4}\right) , ( 3 , 1 3 ) \left(3,\frac{1}{3}\right) has orthocentre at H = ( x , y ) H=(x,y) .

Find y.


The answer is -24.

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1 solution

Soumava Pal
Mar 18, 2016

It is a well known fact that the triangle with vertices with coordinates ( a , c a ) (a,\frac{c}{a}) , ( b , c b ) (b,\frac{c}{b}) , ( d , c d ) (d,\frac{c}{d}) , that is with the vertices lying on a hyperbola, a rectangular hyperbola x y = c = 1 xy=c=1 in this case, the orthocenter of the triangle also lies on the hyperbola x y = c xy=c and is given by ( 1 a b d , c a b d ) (\frac{-1}{abd},-cabd) , and the hyperbola is also known as the Jerabek Hyperbola .

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