Hp 39gii:Using d/dx in solve
05-11-2014, 07:56 PM
Post: #1
 lrdheat Senior Member Posts: 534 Joined: Feb 2014
Hp 39gii:Using d/dx in solve
I just got my 39gii from a dealer in the UK. A trick that I discovered on the TI 36pro works nearly the same on the 39gii...d/dx can be used in the solve app to find a local extremum of f(x)!

On the 39gii, enter the function app and type in your function. Highlight it and copy.

Go to the solve app. select d/dx from the calculus menu (in math key) paste your function inside of (), type in x,x=a put in closing ) and outside of the (), "=0"

Now press num key to get the solve template and make x=0 then solve for a.

This will give the x value of the extremum point which you can now plug into the original equation in the home screen (just paste your function in) go to calculus menu, choose the where symbol, and type x=a.

This works so far for me, even on functions that plot was not finding the local extremum.

When integrating, I find that nroot was not acceptable with some odd number roots, yet integrated when I wrote in, say, a 3root as x^(1/3).

All in all, quite pleased with the calculator, screen resolution is nice, graphing is fast, and especially like not feeling that I have to turn the unit off as quick as possible to save on batteries. It's not a Prime, but works as a big pocketable...it's thicker depth fills a pocket more securely...not as concerned that it will fall out if I lean over as with my Prime.

Like that each command shows syntax guidance on how to properly enter what is required.

Didn't see any indication of connectivity kit on DVD that came with the unit, so I went to the educalc site and downloaded the kit and updated the unit to latest firmware (have to name your unit in setup so that the connectivity kit will find it).
05-13-2014, 08:02 PM
Post: #2
 lrdheat Senior Member Posts: 534 Joined: Feb 2014
RE: Hp 39gii:Using d/dx in solve
Wow! How are you getting your 39 gii to integrate the equation? On my unit, and for that matter, emulator, I get an invalid input if I integrate this particular function with any starting point <1. Any guesses as to what I might doing wrong?

Other functions are working fine...sin(x) 0 to pi produces 2, for example.
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