Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta

(C4 Integration) Quick question - Am I being stupid? watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    Been resolved, thanks!
    Offline

    15
    ReputationRep:
    \frac{x}{x-1}=1+\frac{1}{x-1}...

    (because we can say:

    \frac{x}{x-1}=\frac{(x-1)+1}{x-1}=\frac{x-1}{x-1}+\frac{1}{x-1}
    • Study Helper
    Offline

    15
    Study Helper
    It's rather torturous to read.

    When you say U and U^(-1) cancel out, they in fact multiply to give 1.

    So your integral becomes 1 + U^(-1)
    Offline

    17
    ReputationRep:
    (Original post by The0neAnd0nly)
    Hi there, I am having a little problem with this question, I know the answer is:
    ln(x-1)+x+c

    But I cannot get to it.

    This is the question:

    Integrate this: ∫xx1dx

    This is what I did:

    So let u = x-1
    therefore x = u+1, and du=dx

    So
    (u+1)(u^-1) du

    the U and U^-1 cancel out, so leaves

    ∫u^-1 du, which intergrates to lnu, which is ln(x-1).

    Where does the +x come from!?!?!

    Sorry for the poor layout and thanks in advance!

    x
    x
    First of all, you wrote the question slightly wrong. You mean integral of x((x-1)^(-1)) right?

    The problem is, I don't see how you cancelled (u+1)/u to become 1/u.....
    Offline

    15
    ReputationRep:
    your method gives the integrand as: \frac{u+1}{u}=1+\frac{1}{u}
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by ghostwalker)
    It's rather torturous to read.

    When you say U and U^(-1) cancel out, they in fact multiply to give 1.

    So your integral becomes 1 + U^(-1)

    Thank you, this is the answer I was looking for, For some reason the text came out all wrong...
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: April 2, 2013
Poll
Do I go to The Streets tomorrow night?
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.