Results 1 to 11 of 11

Math Help - Formula for the n-th term . Sequence Question

  1. #1
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Formula for the n-th term . Sequence Question

    Hi, I am new to this forum and I am also very new to math. I failed math in high school so my understanding of algebra is very weak. Even so, I would like to learn so please bare with me if I am being a nuisance.

    Question

    Find formula, showing all the work for the n-th term tn of the sequence (tn) . Defined with

    t1 = 8; tn = ( 5*tn-1 ): 2; *tn-1 = previous term

    I understand a little bit of this

    GCSE Maths Sequences Revision - The nth Term | S-cool, the revision website

    however, I can't seems to relate this with the question I am facing.

    Any help is appreciated

    Thank you for your time
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Oct 2012
    From
    Ireland
    Posts
    591
    Thanks
    159

    Re: Formula for the n-th term . Sequence Question

    Each term is 5 times higher than the previous term, sequences like these are called geometric sequences, since the first term is 8 and the common ratio is 5 the formula for the nth term is 8*5n-1
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Re: Formula for the n-th term . Sequence Question

    Thanks a lot dude! that explains a lot
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Re: Formula for the n-th term . Sequence Question

    Sorry actually I am a bit lost

    If t1 = 8; and tn = (5*tn-1) /2
    Then t3 = (5*20)/2 = 50

    But using the n-th term mentioned wont it be
    t(3) = 8*5^n-1
    = 8*5^2
    = 8*25
    = 400

    I am very new to this, so I'm sorry if i misunderstood you somewhere
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,656
    Thanks
    1604
    Awards
    1

    Re: Formula for the n-th term . Sequence Question

    Quote Originally Posted by RedGuitar View Post
    Sorry actually I am a bit lost
    If t1 = 8; and tn = (5*tn-1) /2
    Then t3 = (5*20)/2 = 50
    But using the n-th term mentioned wont it be
    t(3) = 8*5^n-1
    = 8*5^2
    = 8*25
    = 400
    I am very new to this, so I'm sorry if i misunderstood you somewhere

    Your confusion results from your inability to post clearly what you mean.

    Is it now t_1=8~\&~t_{n}=\left(\frac{5}{2}\right)t_{n-1}~?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Re: Formula for the n-th term . Sequence Question

    The formula given is

    Formula for the n-th term .   Sequence Question-codecogseqn-1-.gif
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,656
    Thanks
    1604
    Awards
    1

    Re: Formula for the n-th term . Sequence Question

    Quote Originally Posted by RedGuitar View Post
    The formula given is

    Click image for larger version. 

Name:	CodeCogsEqn (1).gif 
Views:	0 
Size:	787 Bytes 
ID:	27480

    Why don't you see that \left( {\frac{{5{t_{n - 1}}}}{2}} \right) = \left( {\frac{5}{2}} \right){t_{n - 1}}~?
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Re: Formula for the n-th term . Sequence Question

    Oh I see it now,

    How does sequence is normally solved? Do we eye ball for a pattern or is there a magic formula for it?

    Plato can you please show me step by step to find the n term, please? I've been stuck with this for hours : (.

    I tried to follow this Geometric Sequences and Series but I am still confused.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,656
    Thanks
    1604
    Awards
    1

    Re: Formula for the n-th term . Sequence Question

    Quote Originally Posted by RedGuitar View Post
    How does sequence is normally solved? Do we eye ball for a pattern or is there a magic formula for it?
    {t_n} = 8 \cdot {\left( {\frac{5}{2}} \right)^{n - 1}}
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Newbie
    Joined
    Mar 2013
    From
    Australia
    Posts
    6

    Re: Formula for the n-th term . Sequence Question

    Thanks a lot, I assume nth term = dn + (a - d) comes in play?

    Thank you for your time everyone, it's been a great help
    Follow Math Help Forum on Facebook and Google+

  11. #11
    Super Member
    Joined
    Oct 2012
    From
    Ireland
    Posts
    591
    Thanks
    159

    Re: Formula for the n-th term . Sequence Question

    Quote Originally Posted by RedGuitar View Post
    Thanks a lot, I assume nth term = dn + (a - d) comes in play?

    Thank you for your time everyone, it's been a great help
    That is for an arithmetic sequence, this is a geometric sequence.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. nth term of the sequence help
    Posted in the Advanced Math Topics Forum
    Replies: 7
    Last Post: November 1st 2012, 08:32 PM
  2. Replies: 4
    Last Post: May 13th 2010, 02:59 PM
  3. Formula for nth term of sequence
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: December 23rd 2009, 08:09 AM
  4. Replies: 1
    Last Post: January 22nd 2008, 07:12 PM
  5. Replies: 7
    Last Post: August 31st 2007, 08:18 PM

Search Tags


/mathhelpforum @mathhelpforum