# HP Forums

Full Version: ROOT bug? HP 48S/48G
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

'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

Hi.

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

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.

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.

:)

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

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

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

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

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