Homework Help: geometry

Posted by Zack on Wednesday, October 8, 2008 at 1:18am.

We are learning about proofs. We drew lines between noncollinear points. Our table showed 2 points >> 1 line segment, 3 point >> 3 line segments, 4 points >> 6 line segments, 5 points >> 10 line seg, 6 points >> 15 line seg. etc.

Write an expression in terms of n for the number of line segments that can be drawn between n points.

Please help.

geometry - drwls, Wednesday, October 8, 2008 at 2:01am
1, 3, 6, 10,.. is the series
N*(N-1)/2
where N is the number of points.

These are sometimes refered to as triangle numbers. (This of stacking pop cans in a triangle with rows of 1, 2, 3, 4 etc.)

See http://en.wikipedia.org/wiki/Triangular_numbers
- geometry - Zack, Wednesday, October 8, 2008 at 2:07am
  Thank you very much. I could explain it (I thought) but couldn't express it in math terms. Thanks again
geometry - maria, Friday, December 16, 2011 at 4:20pm
line segment 6cm and divide 5 congruent parts

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