Problem calculating an expression with roots
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02-03-2015, 10:55 AM
(This post was last modified: 02-03-2015 12:26 PM by retoa.)
Post: #27
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RE: Problem calculating an expression with roots
(02-02-2015 12:53 PM)parisse Wrote: ...because the expression is not defined for all values of x (or ambiguous like the definition of x^(1/3) for x<0). Parisse, I agree with you that working with nth roots is not very useful, I think I never found such expressions in real life calculation and it is very difficult to find practical examples with roots above the 3rd (except the 12th root of 2 in music, but you don't have a variable in it). But I still have a question about x^(1/3) for x<0. If I try to calculate (-8)^(1/3), one solution is -2, because (-2)^3=-8 In CAS mode the Prime gives one of the complex solutions, 1+sqrt(3) i In home it gives the complex solution if you enable complex numbers and an error if you don't. 3rd root of (-8) gives -2 (both in home and CAS) Why does the Prime give a complex solution to (-8)^(1/3) and not the trivial one -2? And why does the Prime in home mode not give the -2 solution when it works with real numbers? As a comparison I tried to calculate (-8)^(1/3) on other platforms: HP 11C : Error 0 HP 35s : INVALID y^x (or 1 i sqrt(3) if you use -8 i 0 ) Casio fx82 solar : -2 TI-30X Pro : -2 TI nspire CAS : -2 WP 34S : Domain Error Elektronika MK56 : Error Calculator application in linux mint: -2 Maxima : -2 Wolfram aplha : 1+sqrt(3)i So it seems to be more a philosophical question, cause any producer choose his own way, but would it not be better to give the real solution -2 ? Kind regards Reto |
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