Hi,
All credits goes to Scott Collins  he found this. See his video
https://www.youtube.com/watch?v=iNR7kcA08As
In short:
2 * 2 * 2 = 8
On many calculators cuberoot( 8 ) gives 2...as above.
On the DM42 with CRES enabled this gives:
1.0 + i1.73205...
which is one correct answer.
But with RRES enabled, the cuberoot( 8 ) gives
"Invalid data" (therefore: an error),
which is ... not exactly correct.
What do you think?
Too nerdy or fixable...?
Cheers!
mcc
third root of 8...
third root of 8...
DM 42  SN: 00373, Firmware release v.:3.16. / DMCP 3.20. as compiled by SwissMicros

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Re: third root of 8...
Unless you found an actual cube root function somewhere on the DM42, what you're actually calculating is 8 to the 1/3 power, and that is not a real number. So Invalid Data, in RRES mode, is "exactly correct."
Re: third root of 8...
A few days ago the was nearly the same thread (the last one before this thread): viewtopic.php?f=17&t=2806
It's a programmable calculator
My programmable calculators  former: CBM PR100, HP41CV, HP28S, HP11C  current: HP48G(+), HP35S, DM41X, DM42
Re: third root of 8...
Most calculators will give 2 as a result for 8^1/3...
I'm new to the DM42 (and Free42 for that matter) but I still think that with RRES enabled, "Invalid data" is a wrong answer or, at least, misleading.
Please correct me if I'm wrong.
I'm new to the DM42 (and Free42 for that matter) but I still think that with RRES enabled, "Invalid data" is a wrong answer or, at least, misleading.
Please correct me if I'm wrong.

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Re: third root of 8...
Y to the power 1/X is not the same as the Xth root of Y.
8^(1/3) = e^(ln(8)/3) = 1+i√3. That is not a real number, and therefore Invalid Data is the correct result in RRES mode.
It's not the calculator that is wrong here, but your understanding of mathematics.
Re: third root of 8...
I stand corrected...
...now I wonder why most other calculators show 8^(1/3) = 2
...now I wonder why most other calculators show 8^(1/3) = 2
Re: third root of 8...
One can speculate that it was a philosophical decision by the developers, but I fear it is due to the technical implementation of the routines.
I prefer the results from the 42 because I prefer warnings to halfknowledge. If I see the danger of getting complex results in real algebra, then I deal with the sign at the end of the calculation.
My programmable calculators  former: CBM PR100, HP41CV, HP28S, HP11C  current: HP48G(+), HP35S, DM41X, DM42
Re: third root of 8...
Hi Thomas,
I think a number fell out of your equation, as:
8^(1/3) = e^(ln(8)/3)) = 2e^(i pi/3) = 1+1.7321i
Regards,
Manuel.

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Re: third root of 8...
Re: third root of 8...
Hi Thomas,
Sorry, but in my monitor, the square root symbol appears almost exactly the same as the division one, and that confused me. In fact I had to apply a very big zoom before realizing that you in fact wrote 1+i sqrt(3), and not 1+i/3, as I first read. Sorry again.
Regards,
Manuel.
Sorry, but in my monitor, the square root symbol appears almost exactly the same as the division one, and that confused me. In fact I had to apply a very big zoom before realizing that you in fact wrote 1+i sqrt(3), and not 1+i/3, as I first read. Sorry again.
Regards,
Manuel.