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Math puzzle

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csharp
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  • G Offline
    G Offline
    G Poulose
    wrote on last edited by
    #1

    Check out this gif to know the puzzle: http://gpoulose.home.att.net/untitled.gif George

    J L A 3 Replies Last reply
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    • G G Poulose

      Check out this gif to know the puzzle: http://gpoulose.home.att.net/untitled.gif George

      J Offline
      J Offline
      Joseph Dempsey
      wrote on last edited by
      #2

      I can't even begin to tell you how rusty my math is.... I haven't even had diffy Q's in like 4 years but if you follow the ... logic to its fullest value won't you be takeing some n root of inifinity which is still infinity if memory servers. This should cascade all the way up leaving you with infinity... Please do not shoot the rusty math student! Joseph Dempsey jdempsey@cox.rr.com "Software Engineering is a race between the programmers, trying to make bigger and better fool-proof software, and the universe trying to make bigger fools. So far the Universe in winning." --anonymous

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      • J Joseph Dempsey

        I can't even begin to tell you how rusty my math is.... I haven't even had diffy Q's in like 4 years but if you follow the ... logic to its fullest value won't you be takeing some n root of inifinity which is still infinity if memory servers. This should cascade all the way up leaving you with infinity... Please do not shoot the rusty math student! Joseph Dempsey jdempsey@cox.rr.com "Software Engineering is a race between the programmers, trying to make bigger and better fool-proof software, and the universe trying to make bigger fools. So far the Universe in winning." --anonymous

        G Offline
        G Offline
        G Poulose
        wrote on last edited by
        #3

        Tip: It is a single digit number. George

        E 1 Reply Last reply
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        • G G Poulose

          Tip: It is a single digit number. George

          E Offline
          E Offline
          Eddie Ng 0
          wrote on last edited by
          #4

          Alright I'll give it a try... (do I get any prize? :) ) Let the original expression be X. Then X > sqrt(1 + 3 * sqrt(1 + 4 * sqrt( 1 + 5... ))) Observe that the RHS can be expressed as (X^2 - 1) / 2 Now, Solve the inequality X > (X^2 - 1)/2 <=> 2X > X^2 - 1 <=> (X - 1)^2 < 2 <=> -sqrt(2) + 1 < X < sqrt(2) + 1 However, also we can see from the original expression that X > 1. Since X is an integer, then X must equals to 2. Eddie!

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          • E Eddie Ng 0

            Alright I'll give it a try... (do I get any prize? :) ) Let the original expression be X. Then X > sqrt(1 + 3 * sqrt(1 + 4 * sqrt( 1 + 5... ))) Observe that the RHS can be expressed as (X^2 - 1) / 2 Now, Solve the inequality X > (X^2 - 1)/2 <=> 2X > X^2 - 1 <=> (X - 1)^2 < 2 <=> -sqrt(2) + 1 < X < sqrt(2) + 1 However, also we can see from the original expression that X > 1. Since X is an integer, then X must equals to 2. Eddie!

            G Offline
            G Offline
            G Poulose
            wrote on last edited by
            #5

            Eddie, You are little close to it. >do I get any prize Hey, don't you realize that you had some fun in approaching the puzzle? George

            1 Reply Last reply
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            • G G Poulose

              Check out this gif to know the puzzle: http://gpoulose.home.att.net/untitled.gif George

              L Offline
              L Offline
              Lost User
              wrote on last edited by
              #6

              The puzzle seems to have no solution at all, but... Let's denote the n-th root as x(n): x[n] = sqrt(1+n*x[n+1]), and then x[2] = sqrt(1+2*sqrt(1+3*x[4])), and so on. In other words, x[n+1] = (x[n] - 1)^2/n, and the question of the puzzle is - what is x[2] equal to, if n tends to infinity? It is obvious that the answer depends on how we choose the behavior of x[n]. One possible solution is x[n] = n+1, which gives x[2] = 3, but we can start from any predefined number and construct x[n] so that x[2] will be equal to that number! But if we require that all x[n] are positive, and not growing faster than some power of n, the above "solution" would be the only one. (I guess that if I propose such a solution on a college math exam, they will dismiss me momentarily, but physicists could be satisfied ;) Sorry for long posting - Yuri

              G 1 Reply Last reply
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              • L Lost User

                The puzzle seems to have no solution at all, but... Let's denote the n-th root as x(n): x[n] = sqrt(1+n*x[n+1]), and then x[2] = sqrt(1+2*sqrt(1+3*x[4])), and so on. In other words, x[n+1] = (x[n] - 1)^2/n, and the question of the puzzle is - what is x[2] equal to, if n tends to infinity? It is obvious that the answer depends on how we choose the behavior of x[n]. One possible solution is x[n] = n+1, which gives x[2] = 3, but we can start from any predefined number and construct x[n] so that x[2] will be equal to that number! But if we require that all x[n] are positive, and not growing faster than some power of n, the above "solution" would be the only one. (I guess that if I propose such a solution on a college math exam, they will dismiss me momentarily, but physicists could be satisfied ;) Sorry for long posting - Yuri

                G Offline
                G Offline
                G Poulose
                wrote on last edited by
                #7

                Cool. Thanks for trying. Best, George

                1 Reply Last reply
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                • G G Poulose

                  Check out this gif to know the puzzle: http://gpoulose.home.att.net/untitled.gif George

                  A Offline
                  A Offline
                  Alvaro Mendez
                  wrote on last edited by
                  #8

                  Well, I cheated and wrote a little program to figure it out. ;P The answer is 3 according to this:

                  double recurse(int nValue)
                  {
                  const int nMax = 10000;

                  if (nValue == nMax + 1)
                  	return sqrt(nMax);
                  
                  return sqrt(1 + nValue \* recurse(nValue + 1));
                  

                  }

                  void MathPuzzle()
                  {
                  cout << "Answer: " << recurse(2) << endl;
                  }

                  Regards, Alvaro

                  G 1 Reply Last reply
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                  • A Alvaro Mendez

                    Well, I cheated and wrote a little program to figure it out. ;P The answer is 3 according to this:

                    double recurse(int nValue)
                    {
                    const int nMax = 10000;

                    if (nValue == nMax + 1)
                    	return sqrt(nMax);
                    
                    return sqrt(1 + nValue \* recurse(nValue + 1));
                    

                    }

                    void MathPuzzle()
                    {
                    cout << "Answer: " << recurse(2) << endl;
                    }

                    Regards, Alvaro

                    G Offline
                    G Offline
                    G Poulose
                    wrote on last edited by
                    #9

                    Cool. George

                    1 Reply Last reply
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