What is the maximum area of the triangle in which the points lie?

There are n points in a given plane. Any three of the points form an triangle of area 1 ≤1

For a particular configuration of the points, suppose triangle A B C ABC is the triangle of least area in which all the points lie.

Over all configurations, find the maximum possible area of triangle A B C ABC .


The answer is 4.

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1 solution

Souryajit Roy
May 17, 2014

Among all triples of points,we choose a triple X , Y , Z X,Y,Z such that triangle X Y Z XYZ has the maximal area F F .Obviously F 1 F≤1 .Draw parallels to opposite sides through X , Y , Z X,Y,Z .You get triangle X 1 Y 1 Z 1 X_{1}Y_{1}Z_{1} with area 4 F 4 4F≤4 .We show that triangle X 1 Y 1 Z 1 X_{1}Y_{1}Z_{1} contains all n n points. Suppose there is a point P P outside triangle X 1 Y 1 Z 1 X_{1}Y_{1}Z_{1} .Then triangle X , Y , Z X,Y,Z and p p lie on different sides of at least one of the lines X 1 Y 1 , Y 1 Z 1 , Z 1 X 1 X_{1}Y_{1},Y_{1}Z_{1},Z_{1}X_{1} .From here derive a contradiction.

Hence the answer is 4 4 .

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