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How to find chords, intersections of chords on circle?

  1. Jul 3, 2017 #1
  2. jcsd
  3. Jul 3, 2017 #2


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    The answer gives you the reasons. What do you not understand about that?
  4. Jul 3, 2017 #3
    C-n be the number such chords, why there's 0 chords, 1 chords, then suddenly 3 chords, and 6 chords, how you decide that's gonna be 3, or 6, 10, 15 , or 1? how do you know the order like that?
  5. Jul 3, 2017 #4


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    Because there are 3 ways of linking 2 points out of 3; 6 ways of linking 2 points out of 4, and so on. You can see that from the diagrams; if you don't know the maths, you can just draw the diagrams and count them. Have you studied the mathematics of combinations - how to choose m things from a set of n things? If not, how come you're doing this problem?
  6. Jul 4, 2017 #5


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    Although this thread was marked as being SOLVED, the only solution was in that link and it's clear that you probably do not understand the solution.

    There is a somewhat cleaner expression for the number of regions, rn . You can discover it by considering how rn is related to cn and in for each case listed in that link.

    By The Way;
    Are you familiar with Pascal's triangle?
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