Results 1 to 2 of 2

Math Help - Sigma Notation

  1. #1
    Newbie
    Joined
    Feb 2009
    Posts
    22

    Post Sigma Notation

    My professor started lecture about integrals with sigma notation...i'm having trouble figuring out how to write the following in sigma notation:

    1. 3/5 + 4/6 + 5/7 + 6/8 + 7/9

    2. 1-a+a^2-a^3+a^4-a^5+...+(-1)^n a^n

    For number one I see the pattern but can't make out the right sum notation.

    For number two i got k=0 sigma to n a^k(-1)^k but its wrong I think.

    Any help would be great...
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    Mar 2009
    Posts
    31
    Quote Originally Posted by swimmergirl View Post
    My professor started lecture about integrals with sigma notation...i'm having trouble figuring out how to write the following in sigma notation:

    1. 3/5 + 4/6 + 5/7 + 6/8 + 7/9

    2. 1-a+a^2-a^3+a^4-a^5+...+(-1)^n a^n

    For number one I see the pattern but can't make out the right sum notation.

    For number two i got k=0 sigma to n a^k(-1)^k but its wrong I think.

    Any help would be great...
    Take a look at the first pattern. The denominator is 2 plus the numerator for all terms. Therefore, if the numerator is j, the denominator is j+2. So, the first summations is:

    SIGMA_(j=3 to 7)_[j/(j+2)].

    The second pattern emphasizes a sign change. This is always achieved with (-1)^n, so that if n is odd, the sign is minus (why?) and if n is even, the sign is plus. The first term is 1, or a^0, so it is convenient to start the summation from zero:

    SIGMA_(j=0 to n)_[(-1)^j*(a^j)].
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. sigma notation
    Posted in the Algebra Forum
    Replies: 3
    Last Post: June 24th 2010, 09:35 AM
  2. Sigma Notation Help
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 27th 2010, 12:15 AM
  3. Sigma notation help
    Posted in the Calculus Forum
    Replies: 1
    Last Post: November 29th 2009, 07:07 PM
  4. sigma notation
    Posted in the Calculus Forum
    Replies: 1
    Last Post: November 14th 2009, 04:17 PM
  5. Sigma notation
    Posted in the Algebra Forum
    Replies: 5
    Last Post: January 24th 2008, 03:30 AM

Search Tags


/mathhelpforum @mathhelpforum