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Re: Solve fails

  • To: mathgroup at
  • Subject: [mg33344] Re: Solve fails
  • From: adam.smith at (Adam Smith)
  • Date: Sat, 16 Mar 2002 01:40:31 -0500 (EST)
  • References: <a6rhqq$ep3$>
  • Sender: owner-wri-mathgroup at

The basic problem is that Solve is intended mainly for finding
solutions to linear equations.  Sometimes it works with functions like
Sin and Exp but with the warning that goes something like "Inverse
functions being used - Some solutions may not be found".

In your case however, there is not a clean way to use inverse
functions since the sine function is multiplied by x.

You might have a look at the FindRoot commnad.  It determines a
numerical approximation for the solution.  You doo need to have a
reasonable guess for what the solution is - but it looks like you
already have that.  I don't think you will have any luck finding a
generic, symbolic solution.

Adam Smith

Richard Fateman <fateman at> wrote in message news:<a6rhqq$ep3$1 at>...
> Solve[x*Sin[x]==x*Sin[x^3],x] gives {{}}
> but
> Solve[Sin[x]==Sin[x^3],x]  returns unchanged
> each gives a warning.
> There are very many solutions, among them x=0, x=+-1, 
> x=+-2.0253909752730426 approximately

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