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Math Help - stationary points?

  1. #1
    Junior Member
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    stationary points?

    1. For the following function:


    y= x^3/3+ 2x^2 + 3x - 1



    a. Find the stationary points.
    b. Use the second-order derivatives to test whether the stationary points are at a
    maximum or minimum value of.

    thank you for your help


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  2. #2
    MHF Contributor Also sprach Zarathustra's Avatar
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    a. find f''(x), then x1 and x2 of f'(x)=0
    b. find f''(x), if f''(xt)>0 then xt min. if f''(xt),0 xt max. if f''(xt)=0 and f'''(xt)!=0 then it is nor max/min.
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  3. #3
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    thanks however i am clueless to finding f''(x), then x1 and x2 of f'(x)=0
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  4. #4
    Senior Member yeKciM's Avatar
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    f'_(x)=x^2+4x+3

    when u put f'(x)=0 means that x^2+4x+3=0

    x_1=-1 , x_2=-3 There u have stationary points...

    f''(x)=(f'(x))'=2x+4

    lol... u can go from here ?

    just put stationary points in f''_{(x)}

    f''_{(x_1)}=2 so it's min because it's f''_{(x_1)}>0
    f''_{(x_2)}=-2} so it's max because it's f''_{(x_2)}<0
    Last edited by yeKciM; July 20th 2010 at 08:35 AM.
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