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Topic: Solve results
Replies: 1   Last Post: Oct 30, 1996 12:24 AM

 Messages: [ Previous | Next ]
 Dwarf Posts: 22 Registered: 12/7/04
Solve results
Posted: Oct 25, 1996 10:18 PM

I recently came upon this and was wondering if it's a Solve bug, some
notation I'm not familiar with, or just an unfortunate happenstance.

When I give Mathematica the equation x^3-8==0, this is what it returns:

In[1]:=
Solve[x^3-8==0,x]
Out[1]=
{{x -> 2}, {x -> -2*(-1)^(1/3)}, {x -> 2*(-1)^(2/3)}}

But if I first factor the polynomial instead:

In[2]:=
Solve[Factor[x^3-8]==0,x]
Out[2]=
{{x -> 2}, {x -> (-2 - 2*I*3^(1/2))/2},{x -> (-2 + 2*I*3^(1/2))/2}}

if I use reduce instead of solve

In[3]:=
Reduce[x^3-8==0,x]
Out[3]=
x == 2 || x == (-2 - 2*I*3^(1/2))/2 || x == (-2 + 2*I*3^(1/2))/2

My question is: why the different behaviors, and how can I tell in advance
which to use?

+----------------------------+
| | I understand mine's a risky plan,
| Greg Anderson | and your system can't miss
| dwarf@wam.umd.edu | but is security, after all a cause
| timbwolf@eng.umd.edu | or symptom of happiness.
| |
+----------------------------+ Dream Theater -- A Matter of Time

Date Subject Author
10/25/96 Dwarf
10/30/96 Daniel Lichtblau