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Determining a function with knowledge of it's arc length and it's definite integral

  1. Oct 5, 2010 #1
    Sorry, latex is being weird.

    I'm currently trying to come up with a way to find an equation that satisfies:

    [tex]s=\int_a^b \sqrt{(f'[x])^2+1} \, dx[/tex]

    Which is arc length


    [tex]G=\int_a^b f[x] \, dx[/tex]

    which is area under the curve

    where A and s are known values, and f[a]=A, f=B

    I've tried expressing f[x] as a power series, namely:

    [tex]f[x]=\sum _{n=0}^N a_nx^n[/tex]

    so that:

    [tex]f'[x]=\sum _{n=1}^N n x^{-1+n} a_n[/tex]

    But using that in

    [tex]s=\int_a^b \sqrt{(f'[x])^2+1} \, dx[/tex]

    has proven to be difficult as I am unclear how to square a power series, let alone how to integrate it's root.

    I've also tried adapting the power series into a finite product, namely:

    [tex]\text{Log}\left[\sum _{n=0}^N e^{\left(a_nx^n\right)}\right][/tex]

    Where f'[x] is:

    [tex]f'[x]=\text{Log}\left[\sum _{n=1}^N e^{\left(n a_nx^{n-1}\right)}\right][/tex]

    But I encounter a similar problem, for some r, ln[r]^2 can not be simplified.

    any insight would be greatly appreciated, thanks!
  2. jcsd
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