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# Graph of integral plots, but is invisible

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Prime

Part one:  I'm trying to graph three functions: F2(X), and both it's derivative, F1(X), and its integral, F3(X):

As you can see in the screenshot below, the function [F3(X)] is there, but not only is it invisible, it's value is incorrect for 1/3*X^3  (the value should be: 1/3*(2.051)^3 = 2.8759...).

I've duplicated these functions in the HP Prime Virtual Calculator and got the same result when graphed.  Why is F3(X) invisible, and why is the value incorrect?

Part two:  While troubleshooting this, I tried entering F3(X) different ways.  Instead of typing, "int(F2(X))," I typed "∫X^2,X,a,b"  (with various bounds for (a,b), including (-2,2), (0,2), (1,2), and (0,X)), but each time the graph of it just shows "NaN" for "Not a Number".  What am I doing wrong?

Thank you!

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Hi!, @FailingBetter :

See the images ...

Kind Regards !.
Have a nice day !.
Provost in HP Spanish Public Forum ... https://h30467.www3.hp.com/
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Yes, I can get it to graph 1/3*x^3 by typing it in.  However, the Prime is supposed to be able to graph composite functions entered with reference to other functions.  The User Guide even has a section on doing this with integrals.  I need it to be able to do this, and to do this with the graph visible and calculated correctly.  I’ll contact HP support.

Thanks for trying, Maké!

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Hi!, @FailingBetter :

Allright, but your examples have solutions; however contact with HP Support.

Kind Regards !.
Have a nice day !.
Provost in HP Spanish Public Forum ... https://h30467.www3.hp.com/
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Hello,

This problem is one of my pet peeves 🙂 so please bear with me as I will probably ramble!

What needs to go on the right side of "F1(X)=" is an expression that takes a variable and evaluates to a number.

d(F1(X)/dX does NOT, it evaluates to the derivative of F1(X)

Similarly, int(F1(X)) evaluates to the anti derivative of F1, not to a number.

So, the "proper" way to indicate that you want to graph the derivative of F1 is to use the syntax bellow: d(function(variable))/dvariable=X)

This means that you want to take the derivative of function with regard to variable when/where this variable is equal to X.

People, by habit will write d(F1(X)/dX=X which means take the derivative of F1 with regard to X and evaluate for X = X...

When you say it, it sounds strange, because it highlights the fact that they are 2 different variables, but in this case, we have decided to both call them X!!! there is one variable used for derivating and one variable which is the X used for drawing...

The same applies to the anti derivative... where you need to tell the system that you want to evaluate it between 0 and X. However, for some unkown reason, the use of the same variable name for both variables does not seem to work there... But the following will work...

Anyhow... Another thing that you CAN do is go to the CAS and type F2:=F1' by doing this, you will set F2 to be the derivative of F1 (2*X) and this will fix your problem.

Cyrille

I am an HP Employee
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