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Re: A simple Solve gives me errors

  • To: mathgroup at smc.vnet.net
  • Subject: [mg132630] Re: A simple Solve gives me errors
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Thu, 24 Apr 2014 04:03:14 -0400 (EDT)
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On 4/23/14 at 4:54 AM, stevebg at roadrunner.com (Ste[hen Gray) wrote:

>I want to find the center C of a circle in 3D where the plane is
>defined by points p1,p2,p3. I wrote this:

>eq1 = (ctr - p1).(ctr - p1) - (ctr - p2).(ctr - p2) := 0;
>eq2 = (ctr - p1).(ctr - p1) - (ctr - p3).(ctr - p3) := 0;

>I get errors of a type I've seen before:

You cannot use SetDelayed (:=) in place of Equal (==). You get
the error since SetDelayed is attempting to do precisely what it
is documented to do. That is assign the value 0 to expression on
the left hand side. This clearly isn't what you want and isn't
something Mathematica can do.

Rewrite your definitions for eq1 and eq2 replacing := with ==
and you should get the result you want.




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