Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hi, i have got an awnser to the below question part a, but im not sure if its right and i need help with part b.

    In the binomial expansion, in ascending powers of x, of (1+ax)n, where a and n are constants, the coeffiecnt of x is 15. The coefficient of x2 and x3 are equal.

    a) Find the value of a nad the value of n

    b)find the coefficient of x3

    any help is much appriciated
    Offline

    11
    ReputationRep:
    (Original post by beccajonesy)
    Hi, i have got an awnser to the below question part a, but im not sure if its right and i need help with part b.

    In the binomial expansion, in ascending powers of x, of (1+ax)n, where a and n are constants, the coeffiecnt of x is 15. The coefficient of x2 and x3 are equal.

    a) Find the value of a nad the value of n

    b)find the coefficient of x3

    any help is much appriciated
    So what was your answer for part a)?
    • Thread Starter
    Offline

    0
    ReputationRep:
    i got a=6 and n=2.5
    Offline

    11
    ReputationRep:
    (Original post by beccajonesy)
    i got a=6 and n=2.5
    Me too. :yep:


    So then you can do part b): find the coefficient of x^3 by applying the binomial expansion, substituting in those values. :yes:

    Remember that when n is not an integer, the binomial coefficients are defined without using n! (because n has to be an integer to get a factorial of it):
    \displaystyle \binom{n}{r} = \frac{n(n-1)(n-2)\cdots(n-r + 1)}{r!}
 
 
 
Poll
Cats or dogs?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

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

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

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