Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    find the coefficient of the term in x^3 in the expansion of (2+3x)^3 (5-x)^3
    i have expanded both of them and got
    (8+36x+54x^2+27X^3) and(125-75x+15x^2-x^3)

    i don't know what to do next help
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by yeah1106)
    find the coefficient of the term in x^3 in the expansion of (2+3x)^3 (5-x)^3
    i have expanded both of them and got
    (8+36x+54x^2+27X^3) and(125-75x+15x^2-x^3)

    i don't know what to do next help
    Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by SeanFM)
    Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?
    do you times it together
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by yeah1106)
    do you times it together
    Correct :borat:

    If you are confident, you can save some time by only multiplying things that will get you a coefficient of x^3.
    • Thread Starter
    Offline

    10
    ReputationRep:
    how to know which will give you coefficient of x^3
    Offline

    3
    ReputationRep:
    awwww 4 mins too late ;(

    (Original post by SeanFM)
    Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?
 
 
 

1,087

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should universities take a stronger line on drugs?
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.