ROOT bug? HP 48S/48G « Next Oldest | Next Newest »

 ▼ Eddie W. Shore Posting Freak Posts: 764 Threads: 118 Joined: Aug 2007 07-11-2012, 09:01 AM '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 ▼ Luiz C. Vieira (Brazil) Senior Member Posts: 591 Threads: 16 Joined: Feb 2012 07-11-2012, 09:57 AM Hi. I did not check it, but wouldn't it be a pole? Les Koller Senior Member Posts: 253 Threads: 20 Joined: Jun 2012 07-11-2012, 12:59 PM 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. ▼ Eddie W. Shore Posting Freak Posts: 764 Threads: 118 Joined: Aug 2007 07-11-2012, 02:57 PM 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. ▼ Les Koller Senior Member Posts: 253 Threads: 20 Joined: Jun 2012 07-11-2012, 03:01 PM :) Gilles Carpentier Senior Member Posts: 468 Threads: 17 Joined: May 2011 07-13-2012, 04:03 AM 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. ▼ Les Koller Senior Member Posts: 253 Threads: 20 Joined: Jun 2012 07-13-2012, 05:07 PM Yes, same result on 50G here too, which is what prompted me to go to the Advanced UM. :) Les Koller Senior Member Posts: 253 Threads: 20 Joined: Jun 2012 07-13-2012, 05:17 PM Looks like, from the manual, the 48GX does not have solvevx. Eddie W. Shore Posting Freak Posts: 764 Threads: 118 Joined: Aug 2007 07-13-2012, 07:05 PM 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.

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