Results 1 to 5 of 5

Math Help - Find the sum of the first 5 terms of sequence

  1. #1
    Junior Member
    Joined
    Feb 2007
    Posts
    53

    Find the sum of the first 5 terms of sequence

    Please help, I'm understanding some parts of the sequence and then some parts are confusing. I remember doing these in algebra but they were much simpler. I thought I only had to plug & chug, but...

    I need help with finding the sum of the first 5 terms of the sequence and they are defined recursively by:

    a_{1}=1; a_{2}= 2; \ a_{n}= \ a^2_{n-1} + a^2_{n-2}, \ n\geq3;

    The sum is 1 + 2 + 5 + 29 + 866 = 903.

    I thought the way to do this was to replace n with the numbers 1 - 5:

    a_{1}= a^2_{2-1} + a^2_{2-2} = 1 to get the sum, what I was wrong.

    If I plug in '2' for the next sequence I don't get the right answer. How do I plug in the numbers and solve. I'm confused, please help! TIA...
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by lilrhino View Post
    Please help, I'm understanding some parts of the sequence and then some parts are confusing. I remember doing these in algebra but they were much simpler. I thought I only had to plug & chug, but...

    I need help with finding the sum of the first 5 terms of the sequence and they are defined recursively by:

    a_{1}=1; a_{2}= 2; \ a_{n}= \ a^2_{n-1} + a^2_{n-2}, \ n\geq3;

    The sum is 1 + 2 + 5 + 29 + 866 = 903.

    I thought the way to do this was to replace n with the numbers 1 - 5:

    a_{1}= a^2_{2-1} + a^2_{2-2} = 1 to get the sum, what I was wrong.

    If I plug in '2' for the next sequence I don't get the right answer. How do I plug in the numbers and solve. I'm confused, please help! TIA...
    you are already given a_1 and a_2, no need to find them. all you need to do is find the next 3 terms. so plug in n = 3,4,5 one at a time, and add up all the terms you get with the terms given for a_1 and a_2
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Feb 2007
    Posts
    53
    Quote Originally Posted by Jhevon View Post
    you are already given a_1 and a_2, no need to find them. all you need to do is find the next 3 terms. so plug in n = 3,4,5 one at a time, and add up all the terms you get with the terms given for a_1 and a_2
    I tried to do a_{4} but when I plugged in '4' it didn't equal '29'. I got 3^2 + 2^2 \ which = 13 not 29. Still don't get what I'm doing wrong...
    Follow Math Help Forum on Facebook and Google+

  4. #4
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by lilrhino View Post
    I tried to do a_{4} but when I plugged in '4' it didn't equal '29'. I got 3^2 + 2^2 \ which = 13 not 29. Still don't get what I'm doing wrong...
    a_3 = 5

    so a_4 = a_{4 - 1}^2 + a_{4 - 2}^2 = a_3^2 + a_2^2 = 5^2 + 2^2 = 29
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Feb 2007
    Posts
    53
    Quote Originally Posted by Jhevon View Post
    a_3 = 5

    so a_4 = a_{4 - 1}^2 + a_{4 - 2}^2 = a_3^2 + a_2^2 = 5^2 + 2^2 = 29
    Thanks for your response Jhevon -- I got it!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Fibonaci sequence terms.
    Posted in the Number Theory Forum
    Replies: 9
    Last Post: June 4th 2011, 05:32 AM
  2. Terms in sequence
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: October 13th 2010, 11:26 AM
  3. Replies: 1
    Last Post: May 10th 2010, 03:05 AM
  4. Find terms of a sequence and a formula
    Posted in the Differential Geometry Forum
    Replies: 2
    Last Post: February 16th 2010, 04:52 PM
  5. Replies: 3
    Last Post: December 3rd 2008, 05:42 AM

Search Tags


/mathhelpforum @mathhelpforum