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Math Help - MATHCAD help please

  1. #1
    Newbie
    Joined
    Aug 2009
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    MATHCAD help please

    Hello,
    I have the function f(x)= x(8-5x)(28+5x)/2(2+x)^2
    Interval(0<x<1.6)
    which I have fond the deriviative as
    f'(x) = 1/2x(8-5x)(28+5x)/(2+x)^2
    I found this using simplyfy as when i try to solve symbolically it say no solution.
    Form this I have to solve the equation f'(x)=0 for x to find the maximum of f(x).
    However when I put this into solve back all I come up with is 'Illegal function value '
    Can you show me how to type it in to solve back please. I had a guess at the maximum value being about 0.8 ish.
    Thank you

    I HAVE to use teh solve back facility can't do it any other way because that is what is asked of me in the question.
    Last edited by Tiaan; August 18th 2009 at 04:52 AM.
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  2. #2
    MHF Contributor
    Joined
    Aug 2007
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    USA
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    Thanks
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    1) That's a solve BLOCK. Please read and write more carefully.
    2) What version are you using?
    3) What are you putting in the Solve Block and how are you constructing the block? Did you use the numeric solve or the symbolic solve?

    I couldn't get v14 to have any of the troubles you describe. My first suspicion is the user's familiarity with MathCad. Let's see what you are trying that doesn't work.
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  3. #3
    Newbie
    Joined
    Aug 2009
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    Hi,

    It i called a solve back in my books. I sorted it out Just deleted it all and started again . Thanks anyway
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