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Math Help - finding the stationary points?

  1. #1
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    finding the stationary points?

    I am trying to self teach myself calculus and was wondering if someone could tell me I have done this correctly and got the right answer.

    find the stationary points of this function:
    f(x)=-2x^3-9x^2+24x+40
    so the deriviative is
    f '(x)=6(-x^2-3x+4)

    The stationary points occur where f '(x)=0
    so 6(-x^2-3x+4)=0
    so 6(1-x)(x+4)=0

    so x-1=0 and x+4=0

    x=1 and x=-4

    The satatinary points occur when x=1 and x=-4
    subsitute back into origanal function and the stationary points are:

    (1,53) and (-4,-72)
    If someone could confirm if I am right or where I have gone wrong it would be a great help thanks.
    Last edited by Orlando; March 6th 2012 at 03:08 PM.
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  2. #2
    Senior Member x3bnm's Avatar
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    Re: finding the stationary points?

    > If someone could confirm if I am right or where I have gone wrong it would be a great help thanks.


    Yes you're right. Here's the graph. You can see it yourself in this graph given below.

    finding the stationary points?-graph.jpg

    Hope this helps.
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