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Re: NSolve unable to find all possible roots

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115599] Re: NSolve unable to find all possible roots
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sun, 16 Jan 2011 05:51:39 -0500 (EST)

On 1/15/11 at 4:45 AM, luiz.melo at polymtl.ca (Luiz Melo) wrote:

>The equation below has three possible roots, namely:
>0., 1.99, -1.99.

>eq = x*(Sqrt[-13.319 - x^2] + 2.41*Sqrt[1.004 - x^2])

>If we try NSolve[eq == 0, x], we get {{kx-> 0.}} only.

>How to instruct NSolve to search for the other two roots of the
>above equation?

Given

In[17]:= Sqrt[-13.319 - x^2] + 2.41*Sqrt[1.004 - x^2] /. x -> 1.99

Out[17]= 0. +8.3004 I

And the plot

Plot[{Im[x (Sqrt[-13.319 - x^2] + 2.41*Sqrt[1.004 - x^2])],
   Re[x (Sqrt[-13.319 - x^2] + 2.41*Sqrt[1.004 - x^2])]}, {x,
-2, 2}]

Why is it you think +/-1.99 is a root?



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