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Math Help - finding stationary point again

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    finding stationary point again

    Let f(x) = 3x^4 + 4x^3 - 12x^2 - 24x + 5, x E R ( element of all real numbers)
    f'(x) = 12x^3 + 12x^2 - 24x - 24
    Let f'(x) = 0
    12x^3 + 12x^2 - 24x - 24 = 0
    12[(x+1)(x^2-2)]=0
    therefore x=-1 or x=sqrrt2 or x= -sqrrt 2

    Here's when i am having trouble.
    How do i pick an appropriate start and end point?
    I constructed a table:
    (x) -2 | -1| √1 | √2
    f’(x) -24| 0| -24 | 0


    Why am i getting incorrect values, shouldn't the point before -1 give me a positive tangent instead of a negative one?

    Edit: Solved, thanks anyway.
    Last edited by 99.95; August 11th 2010 at 02:29 AM.
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