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posted by on .

function rule for tis

points- 1 2 3 4
lines- 0 1 3 6

its similar to an earlir one i posted but i still don't quite understand

  • math - ,

    it deals with the number of points that a certain number of lines drawn have.

    BTW, I think you have your headings backwards,
    the first set of numbers should be lines,
    the second set of numbers are the number of intersection points those lines have

    1 line has no intersections points
    2 lines have one intersection points
    3 lines have 3 intersection points
    4 lines have 6 intersection points

    can you see a pattern here?

  • math - ,

    yeaa i understand and can see the patterns i just don't know how to find the function the way you did...

  • math - ,

    I don't know what grade level you are in, so I can't guess how sophisticated the method should be that I describe.

    suppose we double your second line from
    0 1 3 6 ... to
    0 2 6 12 ...
    notice that those are like
    1x0, 2x1, 3x2, 4x3 .... or n(n-1)

    but we multiplied our original numbers by 2, so let's divide our formula by 2 to get back to the originals.

    so the function rule would be
    number of points = n(n-1)/2 , where n is the number of lines drawn.

    If I had 4 lines drawn, n=6
    and no. of intersection points is (6x5)/2 = 15

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