Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Guys, I've been struggling with this question literally all day.
    I would really, really, really appreciate if anyone could explain how to solve it using binomial expansion!

    So here it is:
    When (1- 3/2x)^p is expanded in ascending powers of x, the coefficient of x is -24.


    a) find the value of p
    b) find the coefficient of x^2
    c) find the coefficient of x^3
    Offline

    7
    ReputationRep:
    (Original post by majdalemon)
    Guys, I've been struggling with this question literally all day.
    I would really, really, really appreciate if anyone could explain how to solve it using binomial expansion!

    So here it is:
    When (1- 3/2x)^p is expanded in ascending powers of x, the coefficient of x is -24.


    a) find the value of p
    b) find the coefficient of x^2
    c) find the coefficient of x^3

    So you know about the nCr button on your calculator (related to Pascal's number)?

    You know that the coefficient of x will be the (nCr value)*(-³/2x). The 1 can be ignored since it's always going to be one to any power.

    So let's call the nCr value N.

    N*(-³/2)=-24

    So N=16

    This means for a) p=16 because the first coefficient is always the same as the power it's too. 3C1 gives 3 for example.
    Offline

    7
    ReputationRep:
    (Original post by majdalemon)
    Guys, I've been struggling with this question literally all day.
    I would really, really, really appreciate if anyone could explain how to solve it using binomial expansion!

    So here it is:
    When (1- 3/2x)^p is expanded in ascending powers of x, the coefficient of x is -24.


    a) find the value of p
    b) find the coefficient of x^2
    c) find the coefficient of x^3
    For b)

    Since you know p=16 do 16C2*(-3/2)² which is 270.


    c) 16C3*(-3/2)³=1890


    Does this make sense? Please ask me to clarify things or explain why since I don't know how you've learnt it so far!
    Offline

    19
    ReputationRep:
    It's easier just to expand using the binomial theorem .. and then compare coefficients.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by hippoposthumous)
    For b)

    Since you know p=16 do 16C2*(-3/2)² which is 270.


    c) 16C3*(-3/2)³=1890


    Does this make sense? Please ask me to clarify things or explain why since I don't know how you've learnt it so far!



    THANK YOU SOOSOSOOSSOOSOSOSOSOS MUCH!! You are AMAZING! Thank you!!!!!!!!!!!
    Offline

    7
    ReputationRep:
    (Original post by majdalemon)
    THANK YOU SOOSOSOOSSOOSOSOSOSOS MUCH!! You are AMAZING! Thank you!!!!!!!!!!!
    Ahahha it's a pleasure! I'm glad it was helpful!!
 
 
 
Poll
Do you think parents should charge rent?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

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.