Prime oddity and 39gii

[lrdheat]

Tim W and group...on the Prime in CAS, the integral from 0 to 4 of surd(2*x,3) brings up a message after which alternate solutions of [3 6.00000087595] are presented. 6 is the correct answer. In home, the same integral produces Error: infinity result. In plot mode, area under the curve from 0 to 4 produces "undefined".

On the 39gii, with the function to be integrated entered as (2*x)^(1/3) produces exactly 6. When the function is entered as 3 root (2*x), it produces ER: Invalid input. In plot mode, the area under the curve produces 4.03774125641.

All done on physical devices with latest firmware.

In the classroom, this would produce confusion. Students might not recognize that 4+ is incorrect! For me, lack of confidence (I would prefer an error message over an incorrect result).

[lrdheat]

Addendum...on the prime, when using 3root of 2*x instead of surd(2*x,3), plot and home produce 6.0000000001. CAS still yield problem message and presents the choice I mentioned above. Why isn't surd and alternate method of entry consistent?

[lrdheat]

And more...when entering as (2*x)^(1/3), it produces exactly 6 in home,CAS, and plot. Not intuitive or consistent on Prime, even less so on 39gii.

Neat machines, still needs polishing!

[Mark Hardman]

(05-16-2014 07:58 PM)lrdheat Wrote:  And more...when entering as (2*x)^(1/3), it produces exactly 6 in home,CAS, and plot. Not intuitive or consistent on Prime, even less so on 39gii.

Neat machines, still needs polishing!

This was discussed many months ago in the old forum:

[HP Prime] "Error while checking exact value with approximate value, returning both!"

parisse acknowledges this as a bug at the end of the thread:

"There is an error in the antiderivative of NTHROOT/surd for linear argument explaining the factor 2 errot, I'll fix that. In the meantime use fractional powers..."

Hopefully HP will provide a new firmware revision for the Prime soon. For the 39gii, I would not hold my breath.

Mark Hardman

[lrdheat]

Thanks for the note that this is known on Prime.

Another 39gii deal...

When plotting ((x^2+4)^(1/2))/2 + ((x^2-6*x+10)^1/2))/4, the extremum reduces no minimum or maximum found. When choosing root, it then reports extremum with correct extremum value!, but won't report a root!

[lrdheat]

Same with Prime...if I enter above equation using square root symbol, or using ^(1/2), the plot will not report the roots, but instead reports the extremum when the root is asked for. It will, unlike the 39gii, report the extremum when selected...

[lrdheat]

Duh...no roots to the equation...f(x) never reaches 0.

[lrdheat]

...but why does 39gii not find extremum in plot when extremum is chosen, but finds and reports the extremum when root is selected?

[lrdheat]

New Prime firmware fixed my surd example in CAS, home, and plot. Awesome!

[lrdheat]

Use of 3root(2*x) as opposed to surd(2*x,3) also fixed with new firmware!