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MathGroup Archive 2004

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Re : Solve bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52726] Re : [mg52705] Solve bug?
  • From: "Jaccard Florian" <Florian.Jaccard at he-arc.ch>
  • Date: Sat, 11 Dec 2004 05:21:22 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello !

Your circles have no common points, and the answer is correct on my mathematica version :

In[25]:=
c1 = (-50 + x)^2 + (-50 + y)^2 == 156.25; 
c2 = (-4.5 + x)^2 + (-56.25 + y)^2 == 156.25; 
regle = Solve[{c1, c2}]

Out[27]=
{{x -> 27.25 - 2.6214539372377144*I, 
   y -> 53.125 - 19.08418466309056*I}, 
  {x -> 27.25 + 2.6214539372377144*I, 
   y -> 53.125 + 19.08418466309056*I}}

In[28]:=
c1 /. regle

Out[28]=
{True, True}

In[29]:=
c2 /. regle

Out[29]=
{True, True}

You can see that there are no real solutions using :

In[30]:=
Reduce[{c1, c2}, {x, y}, Reals]

Out[30]=
False

If you want to copy text or graphics from mathematica and paste it in (for example) word, you can "paste special as image" in word.
Or, in mathematica, you can , in the "edit" menu, select "copy as bitmap"! You will be sure that there will be no problem with this bitmap image!


Regards

F.Jaccard
-----Message d'origine-----
De : paul at selfreferral.com [mailto:paul at selfreferral.com] 
Envoyé : vendredi, 10. décembre 2004 02:24
À : mathgroup at smc.vnet.net
Objet : [mg52705] Solve bug?

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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