1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Number Sequences

  1. May 18, 2014 #1
    Hi all

    I'm studying sequences and series, the problem I am having is this:-

    Given the sequence 8 11 14

    Find the Nth Term.

    I have worked out the nth term to be 3N+5, so if I wanted to find the 4th term it would be 3*4+5 = 17.

    The problem is that I have come across the following formula:-

    a+(n-1)d where a = 1st term, N is the Nth term, d common difference.

    If I plug in the values into the above formula I get:-
    8+(4-1)*3 = 17

    I get the same result?? the problem I am having is that I do not understand how the two are related?

    Can someone explain??
     
  2. jcsd
  3. May 18, 2014 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Try expanding the term in parentheses and writing the result in the form A*n+B.
     
  4. May 18, 2014 #3

    Mentallic

    User Avatar
    Homework Helper

    Our sequence is
    a, a+d, a+2d, ...

    which is equivalent to

    a+0d, a+1d, a+2d, ...

    So what we have is:
    1st = a+0d
    2nd = a+1d
    3rd = a+2d
    ...
    nth = a+(n-1)d

    So in order to use a formula that's of this form, we need to make our 1st term (n=1) have a value of 0, n=2 have a value of 1... our nth value have a value of (n-1).

    Hence a+(n-1)d does just this.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Number Sequences
  1. Number Sequence (Replies: 6)

Loading...