Re: Only real solutions for a=a^0.7*b

*To*: mathgroup at smc.vnet.net*Subject*: [mg119729] Re: Only real solutions for a=a^0.7*b*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sun, 19 Jun 2011 07:24:59 -0400 (EDT)*Reply-to*: hanlonr at cox.net

eq = a == a^0.7*b; DeleteCases[ Select[Solve[eq, a], FreeQ[#, Complex] &], _?((a /. #) == 0 &)] {{a -> 1.*b^(10/3)}} DeleteCases[ Select[Solve[Rationalize[eq], a], FreeQ[#, Complex] &], _?((a /. #) == 0 &)] {{a -> b^(10/3)}} Bob Hanlon ---- "niels.gierse at gmail.com" <niels.gierse at googlemail.com> wrote: ============= 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