How to calculate derivatives?

[firedwheelman]

I am having a hard time figuring out how to calculate derivatives on the HP Prime. Do I need to download a certain program or can I compute it directly in CAS mode?

[TheKaneB]

On the first row of keys, under the black portion, you have the following keys: Vars, Tools and Templates (there are graphic icons, not actual words on them).

Click the templates button, select the d/dx template and enter your function by filling up the template provided. Enjoy!
   

In Home view you will get a numerical approximation, while in CAS mode if you have exact mode active you will get a symbolic answer.

[DrD]

Also:

You can use the diff() command (See help): diff(x^2+2*x+c,x) ==> 2*x+2

You can use the apostrophe: (x^2+2*x+c)' ==> 2*x+2

[grsbanks]

(02-20-2018 05:09 PM)DrD Wrote:  You can use the apostrophe: (x^2+2*x+c)' ==> 2*x+2

You learn something new every day -- I never knew that!

[TheKaneB]

That's very useful! In the function definition of the graph app it doesn't work though. You first have to define your f2:=f1' and then apply it to the graph app like F2(X) = f2(X) in the Symbolic view.

[cyrille de brébisson]

Hello,

' for derivative is a CAS function, not a home function which is why it does not work in the plotting app.

2nd subtility.

The "result" of the derivative function is a function, not the function evaluated at a point!
So, if you define F2 in the symb view as der(F1(X),X) (with der being the derivative symbol), whenever F2 gets evaluated, the der function returns the derivated F1, NOT the numerical result of the evaluation of the derivative of F1!

The proper syntax to get the VALUE of the derivative of a function at a point is: der(F1(Y),Y=X).
Note, you could also enter der(F1(X),X=X), which is valid, but confusing to the human because you have 2 X variables here, one used for derivation and one as a numerical value replacement!

Cyrille

[TheKaneB]

Hi Cyrille, thank you for the insight! Really appreciated

[Aries]

(02-20-2018 11:16 AM)firedwheelman Wrote:  I am having a hard time figuring out how to calculate derivatives on the HP Prime. Do I need to download a certain program or can I compute it directly in CAS mode?

Yes, in CAS Mode, there is also a specific template
Best,

Aries :-)