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Two FindRoot questions

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  • Subject: [mg89872] Two FindRoot questions
  • From: Aaron Fude <aaronfude at>
  • Date: Mon, 23 Jun 2008 02:48:44 -0400 (EDT)


These are not FindRoot questions, per se...

Here's a simple example which I want to ask three questions about:

f[k_] := x /. FindRoot[x^2 + k, {x, 0, 10}];
Plot[f[k], {k, -10, 10}]

First, I want the plot to only show where there exists a root.
Is the right solution to make f[] return Null?
How do I make f[] return Null? (Is there a way to "catch" the

Finally, I need to solve my equations to 20 digits. How do I do that?
I've read about Accuracy and Precision but it didn't help.


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