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