Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    I am really not sure what i am doing wrong.
    Find the x co-ordinates of the stationary points of y=xln(x)
    So I started differentiating:

    dy =x* 1/x
    dx

    Which gives 1?
    Then normally you put it equal to 0. 1=0?!

    Thanks for any help
    Offline

    19
    ReputationRep:
    (Original post by shimmyjimmy)
    I am really not sure what i am doing wrong.
    Find the x co-ordinates of the stationary points of y=xln(x)
    So I started differentiating:

    dy =x* 1/x
    dx

    Which gives 1?
    Then normally you put it equal to 0. 1=0?!

    Thanks for any help
    you've used the chain rule instead of the product rule
    the answer is lnx + 1

    as it's 1*lnx + x*1/x
    = lnx + 1

    edit: typo
    • Thread Starter
    Offline

    2
    ReputationRep:
    Cheers guys, you are awesome. Just out of curiosity when you integrate say 4/x, you do get 4ln(x)(+k). So here you dont need to use product rule to get back to 4/x. Why is it different for xln(x)? Is it because its being multiplied by x?
    Cheers
    Offline

    19
    ReputationRep:
    (Original post by shimmyjimmy)
    Cheers guys, you are awesome. Just out of curiosity when you integrate say 4/x, you do get 4ln(x)(+k). So here you dont need to use product rule to get back to 4/x. Why is it different for xln(x)? Is it because its being multiplied by x?
    Cheers
    when you differentiate x, you get 1, which is fine, but 4 gives 0 as a differential.

    in answer to your question, the 4 disappears, it's just ln|x| + c
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 10, 2008

University open days

  • University of Lincoln
    Mini Open Day at the Brayford Campus Undergraduate
    Wed, 19 Dec '18
  • University of East Anglia
    UEA Mini Open Day Undergraduate
    Fri, 4 Jan '19
  • Bournemouth University
    Undergraduate Mini Open Day Undergraduate
    Wed, 9 Jan '19
Poll
Were you ever put in isolation at school?
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.