Re: differences in Solve with -1/2 and -0.5

*To*: mathgroup at smc.vnet.net*Subject*: [mg44396] Re: differences in Solve with -1/2 and -0.5*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Sat, 8 Nov 2003 04:50:41 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <boftfo$5ph$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, the algorithm used by Solve[] divide by zero because it does not see the common exponential factor. Help it with Solve[Simplify[D[x E^(-0.5*x), x]] == 0, x] Regards Jens Kenneth Levasseur wrote: > > Can anyone give a good reason why there is a difference in the > following? Preferably one that my students will understand. > > In[1]:= > Solve[D[x E^(-x/2), x] == 0, x] > Out[1]= > {{x -> 2}} > In[2]:= > Solve[D[x E^(-0.5*x), x] == 0, x] > General::dbyz:Division by zero. > Out[2]= > {} > > Ken Levasseur > Math. Sciences > UMass Lowell