Results 1 to 3 of 3

Thread: Arithmetic Sequence help!

  1. #1
    Newbie
    Joined
    Mar 2009
    Posts
    1

    Arithmetic Sequence help!

    So I was going over some of my Algebra II work and the part that we're going over is COMPLETELY different than the practice problems. We have this question that I didn't even see the directions for how to solve like this:

    What are the missing terms of the arithmetic sequence -8, ___, ___, 3

    I know that the difference is 11 between the two numbers, but I've tried every way possible to get the correct answer. I don't understand how to do it at all. Help, please?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    -1
    e^(i*pi)'s Avatar
    Joined
    Feb 2009
    From
    West Midlands, England
    Posts
    3,053
    Thanks
    1
    Quote Originally Posted by delovely9109 View Post
    So I was going over some of my Algebra II work and the part that we're going over is COMPLETELY different than the practice problems. We have this question that I didn't even see the directions for how to solve like this:

    What are the missing terms of the arithmetic sequence -8, ___, ___, 3

    I know that the difference is 11 between the two numbers, but I've tried every way possible to get the correct answer. I don't understand how to do it at all. Help, please?
    $\displaystyle U_{n} = a + (n-1)d$

    where $\displaystyle U_n$ is the value of term n, $\displaystyle a$ is the first term, $\displaystyle n$ is the number of terms and $\displaystyle d$ is the common difference.

    In your case we have $\displaystyle a = -8$ and $\displaystyle U_4 = 3$

    Putting what is known into the formula:

    $\displaystyle 3 = -8 + (4-1)d $ and it's not hard to see that $\displaystyle d = \frac{11}{3}$

    Therefore your missing numbers are $\displaystyle -8 + \frac{11}{3} = -\frac{13}{3}$ and $\displaystyle -8+2\frac{11}{3} = -\frac{2}{3}$
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    12,028
    Thanks
    849
    Hello, delovely9109!

    Another approach . . .


    What are the missing terms of the arithmetic sequence: -8, ___, ___, 3
    I must assume that you know something about Arithmetic Sequences.


    We have an arithmetic sequence with common difference $\displaystyle d.$

    . . $\displaystyle \begin{array}{cc}\text{The first term is}&\text{-}8 \\ \text{The second term is:}&\text{-}8+d \\ \text{The third term is:}&\text{-}8+2d \\ \text{The fourth term is:}&\text{-}8+3d \end{array}$

    But we already know that the fourth term is $\displaystyle 3.$

    So we have: .$\displaystyle \text{-}8+3d \:=\:3\quad\Rightarrow\quad 3d \:=\:11\quad\Rightarrow\quad d \:=\:\tfrac{11}{3}$


    Therefore, the sequence is: .$\displaystyle \text{-}8,\;\text{-}\tfrac{13}{3},\;\text{-}\tfrac{2}{3},\;3,\;\hdots $

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Arithmetic Sequence
    Posted in the Algebra Forum
    Replies: 4
    Last Post: Apr 21st 2011, 11:27 PM
  2. Arithmetic sequence help?
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: Nov 11th 2010, 03:43 AM
  3. Replies: 2
    Last Post: Aug 24th 2010, 02:10 AM
  4. Arithmetic Sequence
    Posted in the Algebra Forum
    Replies: 1
    Last Post: Nov 19th 2008, 02:10 PM
  5. Replies: 12
    Last Post: Nov 15th 2006, 12:51 PM

Search Tags


/mathhelpforum @mathhelpforum