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Four points on a Plane (Posted on 2004-11-21) Difficulty: 2 of 5
How many ways can four points be arranged in a plane so that the six distances between pairs of points take on only two different values?

  Submitted by Erik O.    
Rating: 4.1429 (7 votes)
Solution: (Hide)
There are 6 ways:

1. The four points form a square.
2. Three points form an equilateral triangle and the fourth point is at the center of that triangle.
3. Points A, B, and C form an equilateral triangle and points D, B, and C form another equilateral triangle.
4. Points A, B, and C form an equilateral triangle, point D sticks out from point A, perpendicular to line BC to a distance equal to the sides on the equilateral triangle.
5. Points A, B, and C form an equilateral triangle. Line AD bisects line BC.
6. The four points make a trapezoid with the base of the trapezoid equal to the diagonals, and the other three lines equal in length.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
answerK Sengupta2007-11-24 05:42:12
So, like, okay ...CeeAnne2004-11-22 15:05:07
noviceTamsyn Lavine2004-11-22 09:09:13
SolutionAnd that is all ...owl2004-11-22 03:09:59
re: What are the defining characteristics ofTomM2004-11-22 01:28:28
re(2): And three moreTomM2004-11-22 01:07:22
What are the defining characteristics of "different arrangements"?David2004-11-22 01:04:47
re(2): And three moreCharlie2004-11-22 00:02:49
re(2): And three moreSteve Herman2004-11-22 00:02:30
Some Thoughtsre: And three moreCeeAnne2004-11-21 22:24:20
Some ThoughtsAnd 3 or 4 trivial solutionsSteve Herman2004-11-21 20:27:33
Some ThoughtsAnd three moreSteve Herman2004-11-21 20:12:09
Some ThoughtsOne MoreCeeAnne2004-11-21 19:33:33
re: Could Become InterestingTomM2004-11-21 19:22:13
Some ThoughtsCould Become InterestingCeeAnne2004-11-21 19:01:22
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