Results 1 to 6 of 6

Math Help - factorial!

  1. #1
    Newbie
    Joined
    Jan 2010
    Posts
    6

    factorial!

    okay, i'm stuck on a couple questions... :/

    2!n! / 4!(n-5) = (n-1)! / (n-4)!

    and..

    (n+2)! / n! = 30


    any help would be great, thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    No one in Particular VonNemo19's Avatar
    Joined
    Apr 2009
    From
    Detroit, MI
    Posts
    1,823
    Quote Originally Posted by needuhelp View Post
    okay, i'm stuck on a couple questions... :/

    2!n! / 4!(n-5) = (n-1)! / (n-4)!

    and..

    (n+2)! / n! = 30


    any help would be great, thanks!
    For the second one \frac{(n+2)!}{n!}=30 means that \frac{(n+2)(n+1)(n)(n-1)(n-2)...}{n(n-1)(n-2)...}=30.

    So by cancelling we get

    (n+2)(n+1)=30

    I'm sure you can finish up. The first is similar, just more messy.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jan 2010
    Posts
    6
    could someone post the work involved with the first question, i'm lost lol
    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 needuhelp View Post
    could someone post the work involved with the first question, i'm lost lol
    post what you tried first
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jan 2010
    Posts
    6
    i have..

    2!(n-1)(n-2)(n-3)(n-4) / 4! = (n-1)(n-2)(n-3)
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by needuhelp View Post
    okay, i'm stuck on a couple questions... :/

    2!n! / 4!(n-5)! = (n-1)! / (n-4)!
    I assume the red factorial was meant to be there.

    This re-arranges into \frac{2!}{4!} = \frac{(n-1)! (n-5)!}{n! (n-4)!}.

    The left hand side is 1/12. Simplify the right hand side using what you have learned from this thread (and what you should have learned from class too) and solve the resulting equation.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. factorial
    Posted in the Number Theory Forum
    Replies: 5
    Last Post: January 8th 2011, 07:42 AM
  2. Sum of Factorial
    Posted in the Calculus Forum
    Replies: 2
    Last Post: January 4th 2011, 12:10 PM
  3. Factorial N
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: August 28th 2010, 10:18 PM
  4. limt with factorial
    Posted in the Calculus Forum
    Replies: 6
    Last Post: June 9th 2009, 08:39 PM
  5. factorial
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 15th 2009, 07:13 AM

Search Tags


/mathhelpforum @mathhelpforum