HP Forum Archive 16

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HP 50g and roots Message #1 Posted by Chuck on 14 Nov 2006, 1:57 a.m. This may have been discussed somewhere before, but anyway.... On the HP 50g if you find the cube root of 15 (in RPN mode, not that it matters) 15^(1/3) I get the traditional "cube root of 15". However if I do the cube root of 16, out pops: e^(4ln(2)/3), which is of course correct, but not the traditional "2 times the cube root of 2". If I find the cube root of 2, and then multiply by 2, it stays "2 times the cube root of 2", not the previous exponential equivalent. Question: is there any way to avoid the exponential form, or avaluate or convert it to the traditional form? This is perplexing me. Also, when you cube the result, the exponential form stays complicated, while the traditional form reverts back to 16. Thanks.

Re: HP 50g and roots Message #2 Posted by James M. Prange (Michigan) on 14 Nov 2006, 3:56 a.m., in response to message #1 by Chuck Well, I did find a round-about way. 16 FACTOR returns '2^4', and then 3 XROOT on that returns '2*XROOT(3,2)', or what looks like 2 times the cube root of 3 in "textbook" display mode or the equation writer. It does seem to me that there ought to be an easier way, but I don't know how. Of course any there are an infinite number of equivalent expressions for anything, and which one is "preferred" or "simplest" often seems somewhat subjective to me. Maybe ask on the newsgroup comp.sys.hp48. Regards, James

Re: HP 50g and roots Message #3 Posted by Marcus von Cube, Germany on 14 Nov 2006, 3:58 a.m., in response to message #1 by Chuck I tried the same on my 40GS (the CAS is the same as that of the 50g.) None of the simplification commands seems to touch the result. It stays in exponential form. I tried real or complex mode both to no avail. It doesn't matter whether you specify 16^(1/3) or the third root of 16. My TI Voyage 200 simplifies the expression to 2*2^(1/3) Marcus

Re: HP 50g and roots Message #4 Posted by James M. Prange (Michigan) on 14 Nov 2006, 4:06 a.m., in response to message #3 by Marcus von Cube, Germany Ah well, it seems to me that Professor Parisse (who wrote the CAS for the 49 series) is rather fond of e and natural logarithms. For me, this often causes "unexpected" (although certainly correct) results, that strike me as being far more complicated than they ought to be. Regards, James

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