Results 1 to 5 of 5

Math Help - sum of 1+cos(x)+...+cos(nx)

  1. #1
    Newbie
    Joined
    Feb 2009
    Posts
    4

    sum of 1+cos(x)+...+cos(nx)

    hi
    i have little problem here with this problem

    i have to find a formula for this sum serie

    1+cos(x)+cos(2x)+cos(3x)+....+cos(nx)

    the hint is i have to use sum of geometric series with the general term e^(ikX)

    thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    13
    there's other way of doing this, or are you really asked to do it by using that hint?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2009
    Posts
    4
    i solved it with the hint
    thanks any way
    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 livan1 View Post
    i solved it with the hint
    thanks any way
    good job. the trick of course was to realize that your sum is the real part of the sum \sum_{k = 0}^\infty e^{i(kx)}, which can be interpreted as a geometric series for which you know the formula.

    Quote Originally Posted by Krizalid View Post
    there's other way of doing this, or are you really asked to do it by using that hint?
    just for fun (and curiosity) what other ways were you thinking of, Kriz?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    13
    Follow Math Help Forum on Facebook and Google+

Search Tags


/mathhelpforum @mathhelpforum