Hey there! Sign in to join this conversationNew here? Join for free

OCR A2 maths january, C3/C4/S2 question. Watch

    Offline

    16
    ReputationRep:
    (Original post by 01234567)
    c3 Jan 2010.

    f(x) = 2 − (√3x + 1)^1/3
    Find the set of values of x for which f(x) = |f(x)|.

    I equated fx to itself and to -fx.. Is this the right way to do the question?
    Not really

    The mark scheme has the answer down as x is less or equal to 7.
    You have to consider the point at which f(x) = 0

    when f(x)>0, |f(x)| does not change so |f(x)|= f(x)

    if f(x)<0, then |f(x)|=-f(x) which is no good to you
    Offline

    16
    ReputationRep:
    (Original post by 01234567)

    5)ii) Find an expression for the second derivative and hence find the value of
    the second derivative at the stationary point.
    I got the right answer up to a point in the mark scheme.
    To find out the second derivative at the stationary point is this the same as just equating dy/dx = 0?
    From the mark scheme, they appear to have substituted x = 0 to find out the stationary point from the equation... so, is this different for the second derivative?
    Difficult to comment without the question
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by TenOfThem)
    Difficult to comment without the question
    link to paper: http://www.ocr.org.uk/images/57765-q...hematics-3.pdf
    Offline

    16
    ReputationRep:
    so, in part (i) you showed that x=0 at the stationary point

    That is why you use x=0
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.