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