Results 1 to 3 of 3

Math Help - Need help understanding summation notation problem...

  1. #1
    Newbie
    Joined
    Nov 2006
    Posts
    2

    Need help understanding summation notation problem...

    So i'm doing some problems in my discrete math book. I ran into this little problem that has a solution in the appendix which I simply do not understand.

    "Write each of 32-41 using summation or product notation.

    32.
    .
    .
    40. n + (n - 1) + (n - 2) + ... + 1
    41."

    The answer in the appendix says:

    (n - i) where i = 0 is the lower limit and n-1 is the upper limit

    I don't get this; that '... + 1' in the problem is throwing me off.

    If you understand this, would you mind explaining this summation form to me.

    Thank you.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,054
    Thanks
    368
    Awards
    1
    Quote Originally Posted by ergoSum View Post
    So i'm doing some problems in my discrete math book. I ran into this little problem that has a solution in the appendix which I simply do not understand.

    "Write each of 32-41 using summation or product notation.

    32.
    .
    .
    40. n + (n - 1) + (n - 2) + ... + 1
    41."

    The answer in the appendix says:

    (n - i) where i = 0 is the lower limit and n-1 is the upper limit

    I don't get this; that '... + 1' in the problem is throwing me off.

    If you understand this, would you mind explaining this summation form to me.

    Thank you.
    What is the value for n - i when i = 0? It's n.
    What is the value for n - i when i = n - 1? It's n - (n - 1) = n - n + 1 = 1.

    So the summation runs over all values from n down to 1.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by ergoSum View Post
    So i'm doing some problems in my discrete math book. I ran into this little problem that has a solution in the appendix which I simply do not understand.

    "Write each of 32-41 using summation or product notation.

    32.
    .
    .
    40. n + (n - 1) + (n - 2) + ... + 1
    41."

    The answer in the appendix says:

    (n - i) where i = 0 is the lower limit and n-1 is the upper limit

    I don't get this; that '... + 1' in the problem is throwing me off.

    If you understand this, would you mind explaining this summation form to me.

    Thank you.
    <br />
n + (n - 1) + (n - 2) + ... + 1=\sum_{i=0}^{n-1} (n-i)<br />

    What the right hand side means is you add all the terms (n-i) for i=0,..,\ i=(n-1).
    These are: when i=0,\ n, when i=1,\ n-1, ..., when i=n-1,\ 1
    If you write this out in full you will find it equals the left hand side.

    RonL
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Understanding Function Notation?
    Posted in the Algebra Forum
    Replies: 1
    Last Post: May 3rd 2011, 10:18 AM
  2. notation - summation
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: September 7th 2009, 02:18 PM
  3. Summation Notation Problem
    Posted in the Algebra Forum
    Replies: 4
    Last Post: February 23rd 2009, 10:17 PM
  4. Summation Notation, Please Help
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: June 14th 2008, 07:22 AM
  5. help understanding this notation
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: April 11th 2008, 01:44 AM

Search Tags


/mathhelpforum @mathhelpforum