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Short Quiz

1. Find \sqrt{1+\sqrt{1+\sqrt{1+\sqrt{1+\sqrt{1+\dots}}}}}.
2. Simplify \frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+\frac{1}{\sqrt{3}+\sqrt{4}}+\dots+\frac{1}{\sqrt{2001}+\sqrt{2002}}+\frac{1}{\sqrt{2002}+\sqrt{2003}}.

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  1. jkyz629
    October 1, 2009 at 9:57 am | #1

    Hint: Try the assumption method in No. 1.

  2. weitar
    October 4, 2009 at 10:50 am | #2

    any clue for question no.2?

    • jkyz629
      October 5, 2009 at 9:11 am | #3

      No. 2 is simply another stereotypical telescopic sum question. However, before doing the summation, some knowledge on surds (search Wikipedia) is required.

  3. weitar
    October 8, 2009 at 2:24 pm | #4

    k i think i know how to do d
    sorry i don know how to type the square root symbol

    1 /1-/2
    —– = —–
    /1-/2 1-2

    then,

    1 1 /1-/2+/2-/3
    —– + —– = ———– = /1-/3
    /1-/2 /2-/3 (1-2)(2-3)

    therefore when continue it to 1/(/2008-/2009), it will become

    (/1-/2)+(/2-/3)+(/3-/4)+…+(/2008-/2009) /1 – /2009
    —————————————– = ———- = /1 – /2009
    (1-2)(2-3)(3-4)……(2008-2009) (-1)^2008

    • weitar
      October 8, 2009 at 2:27 pm | #5

      wah damn ugly..wait i organize again

      1 /1-/2
      ——– = ——–—–
      /1-/2 1-2

      then,

      1 1 /1-/2+/2-/3
      ———– + ———-– = ———–—– = /1-/3
      /1-/2 /2-/3 (1-2)(2-3)

      therefore when continue it to 1/(/2008-/2009), it will become

      (/1-/2)+(/2-/3)+(/3-/4)+…+(/2008-/2009) /1 – /2009
      ——————————————————————-———– = ———- = /1 – /2009
      (1-2)(2-3)(3-4)……(2008-2009) (-1)^2008

  4. weitar
    October 8, 2009 at 2:28 pm | #6

    ok seriously damn ugly…

    just tell the answer enough

    square root of 1 – square root of 2009

    • jkyz629
      October 9, 2009 at 2:55 am | #7

      The answer is supposed to be \sqrt{2009} -1 , which is a negated answer of yours. Notice that
      \frac{1}{\sqrt{1}+\sqrt{2}}=\frac{\sqrt{1}-\sqrt{2}}{1-2}=\sqrt{2}-1

  5. weitar
    October 9, 2009 at 1:31 pm | #8

    oh ya..i did wrongly
    my answer should be (1-/2009)/-1 , which is /2009-1
    k thanks

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