Hey! Sign in to get help with your study questionsNew here? Join for free to post

Finding value independent of x in a binomial expansion?

Announcements Posted on
Take our survey to be in with the chance of winning a £50 Amazon voucher or one of 5 x £10 Amazon vouchers 28-05-2016
  1. Offline


    A = 420
    k = 2

    These were worked out from the earlier part (a)

    What is the method of calculating the independent term ? Someone plz help

  2. Offline

    Find for r=5 (this I did by recognition and some thought...dont really think there is a 'method')

    edit: So
    15C5 k^5 = 3003*32= 96096 I think...
  3. Offline

    ^{15}C_5(x^{10})(\frac{2}{x^2})^  5 = 96096

    I agree with the above post too, just find an r value so that the x terms cancel.
  4. Offline

    what is the r?
  5. Offline

    (x+\frac{k}{x^2})^{15} = \sum_{r=0}^{15} {15 \choose r}x^{15-r}(\frac{k}{x^2})^r
    that is, the fomrula for a binomial expansion, putting n=15

    So the general term is {15\choose r}x^{15-r}(\frac{k}{x^2})^r = {15\choose r}x^{15-r}(kx^{-2})^r

    Can you find a value of r such that the power of x is zero? (Get the x indices together and solve the equation, or just do it by inspection). Evaluate the general term for this value of r.
  6. Offline

    nCr. Number of ways of choosing r objects from n items.


Submit reply


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. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: May 15, 2007
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.

Today on TSR

Don't be a half-term hermit

How to revise this week and still have a life

What's your biggest deadly sin?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read here first


How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

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