Groups > comp.soft-sys.math.mathematica > #3185

Only real solutions for a=a^0.7*b

From	"niels.gierse@gmail.com" <niels.gierse@googlemail.com>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Only real solutions for a=a^0.7*b
Date	2011-06-18 23:54 +0000
Organization	Steven M. Christensen and Associates, Inc and MathTensor, Inc.
Message-ID	<itjdqu$kvd$1@smc.vnet.net> (permalink)

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Hi all!

Is there a way to make Mathematica only report the real solution for

eq = a == a^0.7*b

Solve[eq, a]

reports:
{{a -> 0.}, {a -> (-0.5 - 0.866025 I) b^(
    10/3)}, {a -> (-0.5 + 0.866025 I) b^(10/3)}, {a -> 1. b^(10/3)}}

The solution I am after is the last one. Is there a way to have solve
only report that one? As the exponent is changing from case to case
selecting one like [[5]] does not help. Playing around with Refine[],
Assuming[] etc. to impose a>0 did not help.

Does someone have a hint for me how to do this? I am using Mathematica
7.0.0 (Windows, 64 bit)

Cheers,

Niels

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Only real solutions for a=a^0.7*b "niels.gierse@gmail.com" <niels.gierse@googlemail.com> - 2011-06-18 23:54 +0000

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