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geometry

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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 -

    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 -

    Thank you very much. I could explain it (I thought) but couldn't express it in math terms. Thanks again

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    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?

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