Re: How to avoid complex exponents?

*To*: mathgroup at smc.vnet.net*Subject*: [mg24940] Re: [mg24931] How to avoid complex exponents?*From*: Hugh Walker <hwalker at gvtc.com>*Date*: Thu, 24 Aug 2000 05:08:14 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Peter Chan <y6k at hotmail.com> wrote =============== What is the simplest way to avoid the complex exponents, i.e. exp((-1)^(1/3)) and exp((-1)^(2/3)), given by Mathematica 4.0 in the solution of the following differential equation? Thanks. ----------------------------------------------------- Mathematica 4.0 : In[1]:= DSolve[y''[x]+y'[x]+y[x]==0,y[x],x] 2/3 C[1] (-1) x Out[1]= {{y[x] -> ---------- + E C[2]}} 1/3 (-1) x E ----------------------------------------------------- ============== If you assume all symbols can be taken as real, then what you want is y[x] /. DSolve[y''[x] + y'[x] + y[x] == 0, y[x], x] // First // ComplexExpand == Hugh Walker Gnarly Oaks