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Re: untitled question
*To*: mathgroup at yoda.physics.unc.edu
*Subject*: Re: untitled question
*From*: wmm at chem.wayne.edu (Martin McClain)
*Date*: Thu, 7 Oct 93 11:13:26 EDT
Dear Sergio- Try this:
Eliminate[{ (x-a)^2+(y-b)^2==r^2 ,
x^2+y^2==9 }, {y}] /. a_==b_ -> a-b==0
Then you can pull out the left side and put your own discriminant on it.
Regards- Martin McClain
>I am trying to use Eliminate to eliminate the unknown y in a system of 2 equations:
>
>In[1]:= Eliminate[{ (x-a)^2+(y-b)^2==r^2 ,
> x^2+y^2==9 }, {y}]
>
> 4 2 2 2
>Out[1]= r + r (-18 - 2 a - 2 b + 4 a x) ==
>
> 2 4 2 2 2 4 3 2
>> -81 - 18 a - a + 18 b - 2 a b - b + 36 a x + 4 a x + 4 a b x -
>
> 2 2 2 2
>> 4 a x - 4 b x
>
>
>Is there any way to force Eliminate to produce a result in the form:
>
> expr==0
>
>Or better yet there is any smart way to compute directly the discriminant of the second degree equation
>(in x) Out[1]?
>
>Thank you.
>
>Sergio rescia
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