Results 1 to 11 of 11

Math Help - Arithmetic series

  1. #1
    Newbie
    Joined
    Feb 2008
    Posts
    20

    Arithmetic series

    Find the first four terms of the sequence defined by:
    Un = 4Un-1, U1 = 2
    I know the steps, but i dont know what U2, U3, and U4. I think i someone explained that to me i will be able to do it.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by milan View Post
    Find the first four terms of the sequence defined by:
    Un = 4Un-1, U1 = 2
    I know the steps, but i dont know what U2, U3, and U4. I think i someone explained that to me i will be able to do it.
    Is it not something like

    Un+1 = 4Un-1 ?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2008
    Posts
    20
    Nope, its exactly how i wrote it.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    The way that is written then it is saying that Un = 4Un-1.

    So U1 = 4U1-1
    2 = 4x2 - 1.

    If the formula you have means that the next one in the squence is equal to 4Un-1

    Then you would have 2, (4x2)-1, (4x((4x2)-1)-1.

    Obviously you would simplify the above answer
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,384
    Thanks
    1475
    Awards
    1
    Is not just
    \begin{gathered}<br />
  u_1  = 2 \hfill \\<br />
  u_2  = 4u_1  = 8 \hfill \\<br />
  u_3  = 4u_2  = 32 \hfill \\<br />
  u_4  = 4u_3  = 128 \hfill \\ <br />
\end{gathered} ?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by Plato View Post
    Is not just
    \begin{gathered}<br />
  u_1  = 2 \hfill \\<br />
  u_2  = 4u_1  = 8 \hfill \\<br />
  u_3  = 4u_2  = 32 \hfill \\<br />
  u_4  = 4u_3  = 128 \hfill \\ <br />
\end{gathered} ?
    There is also a -1 after the 4Un.

    I think the confusion is from the fact it normally says Un+1 = ...

    Or the ones I have done in the past have, not sure about anyone else?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Newbie
    Joined
    Feb 2008
    Posts
    20
    Oh, ok, i get it now, i was just a bit stupid haha.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by craig View Post
    The way that is written then it is saying that Un = 4Un-1.

    So U1 = 4U1-1
    2 = 4x2 - 1.

    If the formula you have means that the next one in the squence is equal to 4Un-1

    Then you would have 2, (4x2)-1, (4x((4x2)-1)-1.

    Obviously you would simplify the above answer
    No. The OP means Un = 4U_(n-1) or, even better, Un = 4U_{n-1}.

    You will need to better learn how to interpret poor formatting (which is why users are encouraged to learn basic latex).

    To the OP:

    Quote Originally Posted by milan View Post
    [snip]
    Un = 4Un-1, U1 = 2
    [snip]
    Quote Originally Posted by milan View Post
    Nope, its exactly how i wrote it.
    Nope, it's not exactly how you wrote it. Please take the time to learn some basic latex so that you can format equations more clearly next time. See here: http://www.mathhelpforum.com/math-help/latex-help/
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by mr fantastic View Post
    No. The OP means Un = 4U_(n-1) or, even better, Un = 4U_{n-1}.
    Don't know how you managed 2 work out that it was that lol
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by craig View Post
    Don't know how you managed 2 work out that it was that lol
    Eliminate what doesn't make sense and hopefully you're left with just one interpretation that does (although often that won't be the case, unfortunately).
    Follow Math Help Forum on Facebook and Google+

  11. #11
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,384
    Thanks
    1475
    Awards
    1
    Quote Originally Posted by craig View Post
    Don't know how you managed 2 work out that it was that lol
    The closed form is u_n = 2^{2n-1}.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Arithmetic series.
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: December 20th 2010, 04:03 PM
  2. Arithmetic Series
    Posted in the Calculus Forum
    Replies: 3
    Last Post: September 10th 2010, 01:34 AM
  3. Arithmetic series
    Posted in the Algebra Forum
    Replies: 2
    Last Post: April 6th 2010, 11:24 AM
  4. Sum of Arithmetic Series
    Posted in the Algebra Forum
    Replies: 3
    Last Post: November 26th 2009, 02:25 AM
  5. Arithmetic Progression or Arithmetic Series Problem
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: October 8th 2009, 12:36 AM

Search Tags


/mathhelpforum @mathhelpforum