Results 1 to 2 of 2

Math Help - Need help with Combinatoric Proof

  1. #1
    Newbie
    Joined
    Jan 2010
    Posts
    5

    Need help with Combinatoric Proof

    Hi I need help to find a combinatoric proof regarding :

    2.3^0+2.3^1+...+2.3^{n-1}=3^n -1

    Thanks in advance for the help.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,653
    Thanks
    1478
    Quote Originally Posted by icefirekid View Post
    Hi I need help to find a combinatoric proof regarding :

    2.3^0+2.3^1+...+2.3^{n-1}=3^n -1

    Thanks in advance for the help.
    I take it that the dots are being used to represent multiplication (though if so they should be written higher, using the command \cdot).


    Notice that this is a geometric series, with a = 2, r = 3.


    So S_n = \frac{a(r^n - 1)}{r - 1}

     = \frac{2(3^n - 1)}{3 - 1}

     = \frac{2(3^n - 1)}{2}

     = 3^n - 1.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Even vs. Odd in a combinatoric proof
    Posted in the Number Theory Forum
    Replies: 3
    Last Post: January 2nd 2011, 01:48 AM
  2. Two combinatoric problems
    Posted in the Discrete Math Forum
    Replies: 6
    Last Post: August 21st 2010, 05:16 PM
  3. combinatoric thing
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: April 11th 2008, 12:48 AM
  4. Combinatoric sequence, please help me
    Posted in the Discrete Math Forum
    Replies: 4
    Last Post: September 5th 2007, 08:05 AM
  5. combinatoric identity
    Posted in the Statistics Forum
    Replies: 1
    Last Post: February 17th 2007, 05:24 PM

Search Tags


/mathhelpforum @mathhelpforum