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    Hi there.

    In a scientific paper I have the following equation

    q=aq^3+b [eq1]

    eq1 is approximated with q=a^-0.5 + delta [eq2]

    delta=-b/2

    Where does this approximation come from and why is delta=-b/2?

    Thank you very much.
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    I have updated the first message, since there is some progress.
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    (Original post by Caccioppoli)
    I have updated the first message, since there is some progress.
    Do you have a link to the paper?
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    I haven't a link for the paper which is
    "Application of the Higuchi model for drug release from dispersed
    matrices to particles of general shape" by M. Regina Brophy and P.B. Deasy , 1987

    I've found the solution !!

    we have two equations, basically:

    aq^3-q+b=0 and q=a^{-0.5}+\delta with a small δ

    Writing those two equations in a system, we have that the δ that satisfy both equations is a δ that satisfy this 3rd order equation:

    a\delta^3+3a^{-0.5}\delta^2+2\delta+b=0

    ignoring third order and second order terms in δ we have simply

    2\delta+b=0 so the result \delta=-b/2

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    (Original post by Caccioppoli)
    I've found the solution !!
    Thanks for posting it.
 
 
 
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