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MathGroup Archive 2004

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Re: Solve bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52720] Re: [mg52705] Solve bug?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 11 Dec 2004 05:21:12 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Paul,

When I solve I get complex numbers for solutions.

Solve[{c1, c2}]
{{x -> 27.25 - 2.621453937237714*I, 
   y -> 53.125 - 19.084184663090557*I}, 
  {x -> 27.25 + 2.621453937237714*I, 
   y -> 53.125 + 19.084184663090557*I}}

And when I plot with ImplicitPlot

Needs["Graphics`ImplicitPlot`"]
ImplicitPlot[{c1, c2}, {x, -30, 70}, {y, 0, 70}]

I get two nonintersecting circles.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 

From: paul at selfreferral.com [mailto:paul at selfreferral.com]
To: mathgroup at smc.vnet.net

Solve seems to be returning an invalid answer when I do this:

c1 = (-50 + x)^2 + (-50 + y)^2 == 156.25
c2 = (-4.5 + x)^2 + (-56.25 + y)^2 == 156.25

Solve[{c1,c2}]
{{x -> 16, y -> 43.75}, {x -> 84, y -> 43.75}}

This answer is so wrong!!??
Those two points are completely off. Not even close.

c1 and c2 are the equations of two overlapping circles.
Use ImplicitPlot to verify this fact.
Why can't Mathematica resolve this simple sytem of equations correctly?

If I am doing something wrong please tell me what it is.

Also how can I cut and paste text from a mathematica notebook without
getting all the slashes?
Your help is greatly appreciated.

Regards,
Paul




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