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ROOT bug? HP 48S/48G - Printable Version

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ROOT bug? HP 48S/48G - Eddie W. Shore - 07-11-2012

'X^3+5*X^2-2*X+7'

'X'

0

ROOT


Returns .189254744132. (not a root, f(x) returns about 7)

But using the poly solver...

[1,5,-2,7] gives the correct answers: (approximately)

(.29141, -1.08117), (.29141, 1.08117), -5.58283


Re: ROOT bug? HP 48S/48G - Luiz C. Vieira (Brazil) - 07-11-2012

Hi.

I did not check it, but wouldn't it be a pole?


Re: ROOT bug? HP 48S/48G - Les Koller - 07-11-2012

If you read on the ROOT function of the advanced users manual, it shows you that you enter 1: function 2)variable to solve for 3) guess. The number returned is either the ROOT or the Local EXTREMA. There is a local minimum at x = .189....what your answer was. 0 (your guess) is closer to this value than the actual roots, that's why ROOT gave this answer for this specific guess.


Re: ROOT bug? HP 48S/48G - Eddie W. Shore - 07-11-2012

Quote:
If you read on the ROOT function of the advanced users manual, it shows you that you enter 1: function 2)variable to solve for 3) guess. The number returned is either the ROOT or the Local EXTREMA. There is a local minimum at x = .189....what your answer was. 0 (your guess) is closer to this value than the actual roots, that's why ROOT gave this answer for this specific guess.

Good to know: thank you Les. I'll have to modify my program accordingly.


Re: ROOT bug? HP 48S/48G - Les Koller - 07-11-2012

:)


Re: ROOT bug? HP 48S/48G - Gilles Carpentier - 07-13-2012

Same result with the 50G, using ROOT

Note that on the 50G, in approx mode :
'X^3+5*X^2-2*X+7' SOLVEVX
gave the 3 roots (in complex mode, 1 in real mode)

{ 'X=(.291415279138,-1.08116667823)' 'X=(.291415279138,1.08116667823)' 'X=(-5.58283055828,0.)' }

but is unable to find the exact roots

I don't remember if SOLVEVX exists in 48 series

[link:http://www.wolframalpha.com/input/?i=%27X^3%2B5*X^2-2*X%2B7%3D0%27]Wolfram math[/link]

Edited: 13 July 2012, 4:22 a.m.


Re: ROOT bug? HP 48S/48G - Les Koller - 07-13-2012

Yes, same result on 50G here too, which is what prompted me to go to the Advanced UM. :)


Re: ROOT bug? HP 48S/48G - Les Koller - 07-13-2012

Looks like, from the manual, the 48GX does not have solvevx.


Re: ROOT bug? HP 48S/48G - Eddie W. Shore - 07-13-2012

Quote:
Same result with the 50G, using ROOT

Note that on the 50G, in approx mode :
'X^3+5*X^2-2*X+7' SOLVEVX
gave the 3 roots (in complex mode, 1 in real mode)

{ 'X=(.291415279138,-1.08116667823)' 'X=(.291415279138,1.08116667823)' 'X=(-5.58283055828,0.)' }

but is unable to find the exact roots

I don't remember if SOLVEVX exists in 48 series

[link:http://www.wolframalpha.com/input/?i=%27X^3%2B5*X^2-2*X%2B7%3D0%27]Wolfram math[/link]



I think SOLVEVX started with the HP 49G, not in the 48 series.