Posted by Zack on .
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,
1, 3, 6, 10,.. is the series
N*(N1)/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,
Thank you very much. I could explain it (I thought) but couldn't express it in math terms. Thanks again

geometry 
maria,
line segment 6cm and divide 5 congruent parts

geometry 
Anonymous,
A circle is described by the equation x2 + y2 + 14x + 2y + 14 = 0. What are the coordinates for the center of the circle and the length of the radius?