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   Author  Topic: Angles in GP  (Read 772 times)
Ronno
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Angles in GP  
« on: Mar 2nd, 2009, 7:21pm »
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All points on a plane are colored with three colors. Prove that there exist an infinite number of triangles on the plane with all vertices the same color, that are either isosceles or have their angles in geometric progression.
 
Prove the statement when geometric progression is replaced by arithmetic progression and degenerate triangles are allowed.
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Ronno
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Re: Angles in GP  
« Reply #1 on: Mar 8th, 2009, 11:59pm »
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No takers?
 
The problems are variations of one given in this year's Indian Math Olympiad.
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towr
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Re: Angles in GP  
« Reply #2 on: Mar 9th, 2009, 4:03am »
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Here's a thread that deal with two-colored plane. In that case it applies to any triangle.
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towr
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Re: Angles in GP  
« Reply #3 on: Mar 9th, 2009, 8:45am »
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We can use the idea used at this site.  
It may be interesting to do it without using Van der Waerden's Theorem, using the given properties, but I haven't any ideas.
« Last Edit: Mar 9th, 2009, 8:46am by towr » IP Logged

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Ronno
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Re: Angles in GP  
« Reply #4 on: Mar 9th, 2009, 9:58am »
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Yeah, the problems are similar. Both of these can be solved with 7 points in very symmetric configurations.
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