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Homework Help: Is 2.7177117771117777 irrational?

  1. Oct 14, 2011 #1
    Is 2.71771177711177771111... irrational?

    1. The problem statement, all variables and given/known data
    I'm student teaching 8th graders Numbers and Operations. This is from an 8th grade activity I inherited with no "answer key." Is this decimal (with a pattern but not a repeating pattern) irrational? I am guessing it is, but I want to confirm it. Also, does anyone know if it is a "famous" number?


    2. Relevant equations



    3. The attempt at a solution
    I know that all repeating decimals, such as 2.181818... or 3.156715671567... are rational because they can be represented by fractions a/b, where a and b are integers. And I have studied up on how to convert repeating decimals into fractions. I don't believe this "pattern" in the decimal number in question is "repeating," just a pattern. So I'm thinking it's irrational. But I'm curious about the number itself, also.
     
  2. jcsd
  3. Oct 14, 2011 #2

    gb7nash

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    Re: Is 2.71771177711177771111... irrational?

    Your intuition is correct. The decimal must be repeating the same pattern in order for it to be a rational number. Ergo, this is an irrational number.
     
  4. Oct 14, 2011 #3
    Re: Is 2.71771177711177771111... irrational?

    Thanks! And you didn't recognize it, did you, as a well-known number?
     
  5. Oct 14, 2011 #4

    gb7nash

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    Re: Is 2.71771177711177771111... irrational?

    I don't know. I've never seen it.
     
  6. Oct 14, 2011 #5

    ehild

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    Re: Is 2.71771177711177771111... irrational?

    It is somewhat close to e=2.7182818284590....

    ehild
     
  7. Oct 14, 2011 #6
    Re: Is 2.71771177711177771111... irrational?

    Thanks, ehild and gb7nash! I wish I could think of how such a pattern could be generated. WTMTOMH, I guess.
     
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