Results 1 to 3 of 3

Math Help - series

  1. #1
    Member
    Joined
    Nov 2008
    Posts
    79

    series

    "Find s_3 , the third term in the series which corresponds to the geometric sequence which has a = 8 and r = 1/4"

    I'm not sure what the method is in order to work out what s_3 is..
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member pberardi's Avatar
    Joined
    Dec 2008
    Posts
    85
    Quote Originally Posted by 14041471 View Post
    "Find s_3 , the third term in the series which corresponds to the geometric sequence which has a = 8 and r = 1/4"

    I'm not sure what the method is in order to work out what s_3 is..
    The formula for finding the nth Term of a Geometric Sequence is
    a_n = a_1*r^(n-1)

    I am going to just assume that you made a typo and that your a = 8 is really a_1 = 8. If not please disregard.

    a_3 = 8*(1/4)^(2)
    a_3 = 8*(1/16)
    a_3 = 1/2
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    28
    S_n = \frac{a(1-r^n)}{(1-r)}

    S_3 = \frac{8(1-\frac{1}{4}^3)}{(1-\frac{1}{4})}

    S_3 = \frac{21}{2}


    also S_3 = a_1+a_2+a_3

    S_3 = 8+2+\frac{1}{2}= \frac{21}{2}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: October 3rd 2011, 01:12 AM
  2. Replies: 3
    Last Post: September 29th 2010, 06:11 AM
  3. Replies: 0
    Last Post: January 26th 2010, 08:06 AM
  4. Replies: 2
    Last Post: December 1st 2009, 12:45 PM
  5. Replies: 1
    Last Post: May 5th 2008, 09:44 PM

Search Tags


/mathhelpforum @mathhelpforum