Re: solve for a squared variable
- To: mathgroup at smc.vnet.net
- Subject: [mg60469] Re: solve for a squared variable
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sat, 17 Sep 2005 02:31:50 -0400 (EDT)
- Organization: The Open University, Milton Keynes, U.K.
- References: <200509150916.FAA15860@smc.vnet.net> <dgduk1$19t$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Ruth Lazkoz wrote:
> Hi everyone,
>
> Why does
>
> Solve[x^2 + y == 1, x^2]
>
> give and error message? How can I solve for x^2?
>
> Thanks,
>
> Ruth
>
Hi Ruth,
Since the error message is
_General::ivar : x^2 is not a valid variable. More..._
so we must do a change of variable as in the following example:
In[1]:=
expr = x^2 + y == 1
Out[1]=
x^2 + y == 1
In[2]:=
Solve[expr /. x^2 -> X, X]
Out[2]=
{{X -> 1 - y}}
In[3]:=
x -> Sqrt[X /. %[[1]]]
Out[3]=
x -> Sqrt[1 - y]
In[4]:=
expr /. %
Out[4]=
True
Regards,
/J.M.
- References:
- Re: Why this function does not return a single value
- From: Bill Rowe <readnewsciv@earthlink.net>
- Re: Why this function does not return a single value