Re: Help with Solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg112388] Re: Help with Solve*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 12 Sep 2010 03:12:03 -0400 (EDT)

On 11 Sep 2010, at 11:46, Eduardo Cavazos wrote: > On Sep 9, 3:23 am, Eduardo Cavazos <wayo.cava... at gmail.com> wrote: > >> Here's a couple of equations: >> >> eq1 == n*Sin[x] ==== (m*v^2)/r; >> eq2 == n*Cos[x] ==== m*g; >> >> The goal is to solve for 'x'. >> >> I can do this in a roundabout way via: >> >> Solve[eq1 /. Solve[eq2, n], x] > > I should point out that the answer that I get from using Solve this > way is: > > {{x -> ArcTan[v^2/(g r)]}} > > which is form the answer I'm looking for. :-) Again, I'm just > wondering if Mathematica can do the work for me, instead of having to > manually eliminate 'n' in a separate step. > > Sjoerd and Bob recommended using Reduce. Thanks for the tip! I tried > to use Reduce but the results it produced were not in the above form. > > Ed > You can tell Solve to eliminate n before solving for x: Solve[{eq2, eq1}, x, n] (The answers are expressed in terms of ArcCos instead of ArcTan but are essentially equivalent to the one you got. Of course using Solve, unlike Reduce, not give you a complete solution) Andrzej Kozlowski