Missing one root

12132020, 01:07 AM
Post: #1




Missing one root
Hello,
I'm going over some simple math problems on both my HP50G and my Prime. When I try to solve the very simple equation (x3)^(2/3) = 4 The HP50G correctly provides 11 and 5 as answers within a list However the Prime only finds 11 as root, also within a list. What gives? Thanks for reading. 

12132020, 01:38 AM
Post: #2




RE: Missing one root
Try using surd for the 1/3 power.
Cas> solve((surd(x3,3)^2) = 4,x) → {5,11} 

12132020, 02:52 AM
Post: #3




RE: Missing one root  
12132020, 03:45 AM
(This post was last modified: 12132020 03:56 AM by victorvbc.)
Post: #4




RE: Missing one root
(12132020 02:52 AM)rrpalma Wrote: Thanks!!! It worked. By using the fractional exponent "1/3" the Prime returns the principal cube root, which in this case will be a complex number for any x<3. Whereas using surd or NTHROOT it returns the realvalued root instead, allowing for a zero at x=5 in the equation (x3)^(2/3)4=0. Edit: Wolfram Alpha for reference: https://www.wolframalpha.com/input/?i=%2...3%294%3D0 If you want to assume the realvalued root on the Prime, always use the root template key, nthroot, or equivalent. 

12132020, 04:33 AM
Post: #5




RE: Missing one root
(12132020 03:45 AM)victorvbc Wrote:(12132020 02:52 AM)rrpalma Wrote: Thanks!!! It worked. Thanks. Very much appreciated. I tried it both with NTHROOT and the template, and it worked. I'm still confused on why HP50G directly provides the realvalued root(s) whereas the Prime doesn't. I guess that's the way it is, and that's it. Or, how do I force then the HP50G to provide only the principal root? 

12162020, 02:12 AM
(This post was last modified: 12162020 02:20 AM by cdmackay.)
Post: #6




RE: Missing one root
(12132020 04:33 AM)rrpalma Wrote: Or, how do I force then the HP50G to provide only the principal root? I had thought that setting system flag 1 "principal value" might do it; but no, not with SOLVE. Whereas if you use ISOL (isolate), it does honour the flag, but shows X=5 only Cambridge, UK 41CL/DM41X 12/15C/16C DM15/16 71B 17B/II/II+ 28S 42S/DM42 32SII 48GX 50g 35s WP34S PrimeG2 WP43S/pilot Casio, Rockwell 18R 

12162020, 03:37 AM
Post: #7




RE: Missing one root
(12162020 02:12 AM)cdmackay Wrote:(12132020 04:33 AM)rrpalma Wrote: Or, how do I force then the HP50G to provide only the principal root? Thanks!! That's really odd :) 

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