Results are out! Find what you need...fast. Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Factorials C2

Announcements Posted on
Will you get the grades you need for uni? Get prepared today and de-stress, sign up to email alerts for course places! 02-06-2015
Waiting on IB results? Our IB results hub explains everything you need to know 01-06-2015
  1. Offline

    ReputationRep:
    Hi all, I'm working on sequences today however my textbook is not very clear on the topic of factorials. It gives very few examples. I am currently working through the questions at the end of the section but I am confused with the following:

    Express as a factorial:

    n(n^2-1)
    8x7!

    Apologies is these are very basic questions but the book only gives basic examples and explanation e.g. 8!/7!

    If you could explain to me how I should approach Q's like that it would be much appreciated
  2. Offline

    ReputationRep:
    You need to express 8 x 7! as a factorial?

    The answer is 8!
  3. Offline

    ReputationRep:
    Ok I get that, 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 but how do I approach the other Q:

    n(n^2-1) as a factorial
  4. Offline

    ReputationRep:
    (Original post by vinvinvin)
    Hi all, I'm working on sequences today however my textbook is not very clear on the topic of factorials. It gives very few examples. I am currently working through the questions at the end of the section but I am confused with the following:

    Express as a factorial:

    n(n^2-1)
    8x7!

    Apologies is these are very basic questions but the book only gives basic examples and explanation e.g. 8!/7!

    If you could explain to me how I should approach Q's like that it would be much appreciated

    I hope this is want you want


    Uploaded with ImageShack.us
  5. Offline

    ReputationRep:
    (Original post by vinvinvin)
    Ok I get that, 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 but how do I approach the other Q:

    n(n^2-1) as a factorial
    Factorise

    n^2-1
  6. Offline

    ReputationRep:
    (Original post by steve2005)

    I hope this is want you want


    Uploaded with ImageShack.us
    Apologies for not being clear, they were two separate questions. Thanks for the input though.
  7. Offline

    ReputationRep:
    (Original post by vinvinvin)
    Hi all, I'm working on sequences today however my textbook is not very clear on the topic of factorials. It gives very few examples. I am currently working through the questions at the end of the section but I am confused with the following:

    Express as a factorial:

    n(n^2-1)
    8x7!

    Apologies is these are very basic questions but the book only gives basic examples and explanation e.g. 8!/7!

    If you could explain to me how I should approach Q's like that it would be much appreciated
    The key is to recognise what a factorial is - it is simply the multiplicative equivalent of a series summation.

    i.e. n! = 1x2x3x4x...x(n-1)xn

    you multiply all the numbers from 1 to n (inclusive) together.

    so to do 8 x 7!

    7! = 1x2x3x4x5x6x7
    multiply by 8
    1x2x3x4x5x6x7x8

    which is, just by looking at it, 8!

    equally, if you want to do a!/b!, with b<a,
    a! = 1x2x...xbx(b+1)...xa
    b! = 1x2x...xb

    cancelling all the terms that match leaves only (b+1)x(b+2)x....xa

    for n(n^2-1)

    recognise using difference of two squares that (n^2-1) = (n+1)x(n-1)
    so you want to express (n-1) x n x (n+1) in factorial terms (find suitable a and b such that a!/b! gives this)
  8. Offline

    ReputationRep:
    (Original post by The Mr Z)
    The key is to recognise what a factorial is - it is simply the multiplicative equivalent of a series summation.

    i.e. n! = 1x2x3x4x...x(n-1)xn

    you multiply all the numbers from 1 to n (inclusive) together.

    so to do 8 x 7!

    7! = 1x2x3x4x5x6x7
    multiply by 8
    1x2x3x4x5x6x7x8

    which is, just by looking at it, 8!

    equally, if you want to do a!/b!, with b<a,
    a! = 1x2x...xbx(b+1)...xa
    b! = 1x2x...xb

    cancelling all the terms that match leaves only (b+1)x(b+2)x....xa

    for n(n^2-1)

    recognise using difference of two squares that (n^2-1) = (n+1)x(n-1)
    so you want to express (n-1) x n x (n+1) in factorial terms (find suitable a and b such that a!/b! gives this)
    That is a fantastic help thank you, it's all clear now.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: April 1, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

New on TSR

Improving your uni offer

Why now is the time to think about Adjustment

Study resources
x

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.