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-   -   Infinite surd (https://www.askmehelpdesk.com/showthread.php?t=430443)

  • Jan 1, 2010, 11:48 PM
    8below1994
    infinite surd
    The sequence:
    a1=√(1+√(1 )
    a2=√(1+√(1+√(1 )
    a3=√(1+√(1+√(1+√(1+... etc.

    Calculate the decimal values of the first ten terms of the sequence. Using technology plot the relation between n and an. Describe what you notice. What does this suggest about the value of (a(n))-(a(n+1)) as n gets very large? Use your results to find the exact value for this infinite surd.
  • Jan 2, 2010, 12:03 AM
    Unknown008

    If I got it right;



    You'll have to grab a calculator for that, and find the value of each of the 10 terms.

    For the second part, I can't help you. Apparently, you have a program which can plot the points of the sequence. Sorry.

    For the third part, it's easy if you have plot the graph. You'll see that the value tends to be a constant and the graph makes an asymptote. I'll let you guess the answer to that.

    Is it OK?:)
  • Jan 2, 2010, 12:07 AM
    8below1994

    Makes sense, but what is the formula for a(n+1) in terms of a(n) ?
  • Jan 2, 2010, 12:13 AM
    Unknown008

    Sorry, I don't see the question asking for the formula.

    Think a little more now. If the terms approach a certain number, it means that they are nearly the same number, or roughly the same number if n is extremely large.

    So, a_n is a term, where n is very large
    a_(n+1) is the term just after a_n.

    Can you see where I'm getting at?
  • Jan 2, 2010, 12:14 AM
    8below1994

    Its making more sense... I asked a broader question... check that?
  • Jan 2, 2010, 05:09 AM
    galactus

    This is the nested radical form for the Golden Ratio.

    Let L equal the limit. Then, since it is nested and convergent, we can write:







    If we let

    We get
  • Jan 2, 2010, 11:19 AM
    Unknown008

    galactus, can you have a look at the other thread. It's in the same board and it's by the same member.
  • Jan 2, 2010, 12:08 PM
    galactus

    Let's do something general.

    Start with

    and assume it converges when .







    Using the quadratic formula, we get



    Now, for the given nested radical, a=b=1.

    Therefore,



    The Golden Ratio, commonly designated as

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