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From: Bill Rowe <readnews@sbcglobal.net>
Newsgroups: comp.soft-sys.math.mathematica
Subject: Re: A simple Solve gives me errors
Date: Thu, 24 Apr 2014 08:03:16 +0000 (UTC)
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On 4/23/14 at 4:54 AM, stevebg@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.