How to calculate derivatives?

[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