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