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I have some data and I'd like to calculate the radius of curvature. The formula is: $$R_{oc}\space Sinh\left[\frac{D_{LSS}}{R_{OC}}\right]=\frac{s_*}{\theta_*}$$ Noting that $s_*$ is sh, $\theta_*$ is angle,$D_{LSS}$ is distance, $R_{OC}$ is Roc, I tried using Solve to solve the equation:

Solve[Roc*Sinh[distance/Roc] == sh/angle, Roc]

and got:

Solve::nsmet: This system cannot be solved with the methods available to Solve.

So I tried supplying some values and doing it numerically:

sh = 7.74*^21; 
angle = 1.0411/100.; 
distance = 5.32*^23;
NSolve[Roc*Sinh[distance/Roc] == sh/angle, Roc]

And I got the equation spit back out at me. Can someone help me solve this equation either analytically or numerically?

Note: I suspect a third option might be to use optimization, but I just can't figure out how to set up the function.

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  • 4
    $\begingroup$ That doesn't look like an equation with a closed form solution. You'd need FindRoot[] with a good starting point for this. $\endgroup$ – J. M.'s discontentment May 10 at 16:48
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Clear["Global`*"]

sh = 774*^19;
angle = 10411*^-6;
distance = 532*^21;

arg = NArgMin[
   {(Roc*Sinh[distance/Roc] - sh/angle)^2, Roc > 10^20},
   Roc, WorkingPrecision -> 30] // N

(* 3.63412*10^23 *)

FindRoot[
 Roc*Sinh[distance/Roc] == sh/angle,
 {Roc, 10^23}]

(* {Roc -> 3.63412*10^23} *)

NSolve[
  {Roc*Sinh[distance/Roc] == sh/angle,
   10^22 < Roc < 10^24}, Roc][[1]]

(* {Roc -> 3.63412*10^23} *)
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