Turn on thread page Beta

need help on these two questions! binominal exapnsion. please! watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    1.) find the coefficient of x^4 in the expansion of (1+3x)^7
    2.) complete the first 3 terms in the bionominal expansion of (1=6x)^9
    use thee terms to find an approximate value for (1.06)^9 correct to 3dp

    please need the answers... would be so gratefull
    Offline

    6
    ReputationRep:
    Show us your working
    • Thread Starter
    Offline

    0
    ReputationRep:
    my working i like tooo long and complicated i used the rule:
    1+nx+n(n-1)x^2+n(n-1)(n-2)x^3
    but still semm to get it wrong and confused
    • Thread Starter
    Offline

    0
    ReputationRep:
    i got a answer of 840 x^4 for the first 1 :/
    Offline

    14
    ReputationRep:
    (Original post by Humii)
    my working i like tooo long and complicated i used the rule:
    1+nx+n(n-1)x^2+n(n-1)(n-2)x^3
    but still semm to get it wrong and confused
    You don't appear to be dividing by factorials.

    1+nx+n(n-1)x^2/2! +n(n-1)(n-2)x^3/3!
    • Thread Starter
    Offline

    0
    ReputationRep:
    yh, i did but didnt knw hw to write it on here
    Offline

    0
    ReputationRep:
    first one (sorry havent got my calculator so cant work out) is 7C4 x 1^3 x 3^4 x (x)^4

    second one is 1 + 9 x 1 x 6x + 9C2 x 1 x 6^2 x (x)^2

    for the second part of two u make (1+6x) = 1.06 so x = 0.01, and then u substitue x into the equation above, so 1 + 9 x 1 x 6(0.01) etc... and this should give u an answer to (3.d.p)

    hope this helps
 
 
 

University open days

  • University of Warwick
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • University of Sheffield
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 20 Oct '18
Poll
Who is most responsible for your success at university
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

Equations

Best calculators for A level Maths

Tips on which model to get

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.