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    (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

    (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

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

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

    That is why you use x=0
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