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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
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    (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
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    (Original post by TenOfThem)
    Difficult to comment without the question
    link to paper: http://www.ocr.org.uk/images/57765-q...hematics-3.pdf
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    so, in part (i) you showed that x=0 at the stationary point

    That is why you use x=0
 
 
 
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