How to instruct Math to take a certain (e.g. real) type of results
- To: mathgroup at smc.vnet.net
- Subject: [mg105018] How to instruct Math to take a certain (e.g. real) type of results
- From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
- Date: Wed, 18 Nov 2009 06:57:41 -0500 (EST)
I came to a problem, that I cannot check the solution y=0 of equation
In:= eq = (-8 + y)^(1/3) + (8 + y)^(1/3) == y^(1/3);
eq /. y -> 0
just because the expression
In:= eq[] /. y -> 0
Out= 2 + 2 (-1)^(1/3)
Mathematica does not interpret as zero. And if I ask it to give a
In:= 2 + 2 (-1.)^(1/3)
Out= 3.+ 1.73205 \[ImaginaryI]
It returns the complex root out of the three possible.
My question is the following:
1) How should I instruct Mathematica to take a certain root that I want
of say, (-1)^(1/3)?
2) I think there is a general possibility instruct Mathematica that all
calculations should be done on reals only. Is it right?
Thank you, Alexei
Alexei Boulbitch, Dr., habil.
11, rue Edmond Reuter
Phone: +352 2454 2566
Fax: +352 2454 3566
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