A simple Solve gives me errors

*To*: mathgroup at smc.vnet.net*Subject*: [mg132628] A simple Solve gives me errors*From*: "Ste[hen Gray" <stevebg at roadrunner.com>*Date*: Wed, 23 Apr 2014 04:54:08 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

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: p1 = {p1x, p1y, p1z}; (* tell it that p1,p2,p3 are vectors *) p2 = {p2x, p2y, p2z}; (* center of circle ctr = f p1+g p2+(1-f-g)p3 *) p3 = {p3x, p3y, p3z}; (* keep the center in the plane of p1,p2,p3 *) ctr = f p1 + g p2 + (1 - f - g) p3; 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: SetDelayed::write: Tag Norm in Norm[{-p1x+f p1x+g p2x+(1-f-g) p3x,-p1y+f p1y+g p2y+(1-f-g) p3y,-p1z+f p1z+g p2z+(1-f-g) p3z}] is Protected. >> And a similar one. I don't know what to do about this. I want to do Solve[{eq1, eq2}, {f, g}]

**Follow-Ups**:**Re: A simple Solve gives me errors***From:*Murray Eisenberg <murray@math.umass.edu>