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Full Version: HP Prime - Defining a function
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How can i define a function for example f(x) = x^2 +8x +4 in den Home-Screen, then calculate f(1), f(2).

Then i want to build the derivate of f(x) in CAS.

Then i want go plot the graph of f(x) and the derivate f'(x).

How can i do this things?

I do this like this :

```To define f :
CAS then f(x):=x²+8*x+4
To calculate f(1), f(2) . CAS or HOME, and just
f(1)  or  f(2)
To built the derivative, CAS, then
g:=f'
To plot
APPS FUNCT
F1   f(X)   // be carefull about X and not x
F2   g(X)
Plot
Not that :
F2   f'(X)  doesn't work
Perhaps there are other ways ...
```

Edited: 22 Oct 2013, 5:59 p.m.

Quote:
I do this like this :
```To define f :
CAS then f(x):=x²+8*x+4
To calculate f(1), f(2) . CAS or HOME, and just
f(1)  or  f(2)
To built the derivative, CAS, then
g:=f'
To plot
APPS FUNCT
F1   f(X)   // be carefull about X and not x
F2   g(X)
Plot
Not that :
F2   f'(X)  doesn't work
Perhaps there are other ways ...
```

```F1:=f('X'); // need ' ' when using global, built-in, non-CAS variables
F2:=f'; // more direct; auto-converts x to X
F2:=f'('X'); // more explicit
```

Edited: 22 Oct 2013, 10:28 p.m.

Thank's !

```F1:=f
F2:=f'
```
works fine ;)

Edited: 23 Oct 2013, 4:10 a.m.

1. There is no „:=“ key similary to TI NSPIRE.

2. In CAS the function-letter will be automatically lower case (f) and in HOME screen and in APPS FUNC the function letter will be automatically upper case (F) so that i have another keystroke (Shift) for lower case (f)

3. The small x and the big X in CAS/APPS FUNC are confusing.

Questions:

1. How can i reach the ' in the derivate?

2. What is the logic behind the lower case/upper case X/x F/f?

Quote:

1. There is no „:=“ key similary to TI NSPIRE.

2. In CAS the function-letter will be automatically lower case (f) and in HOME screen and in APPS FUNC the function letter will be automatically upper case (F) so that i have another keystroke (Shift) for lower case (f)

3. The small x and the big X in CAS/APPS FUNC are confusing.

Questions:

1. How can i reach the ' in the derivate?

2. What is the logic behind the lower case/upper case X/x F/f?

1. := can be obtained typing each character using [Alpha][-][Shift][.]

2. Single, capital letters are global, real-valued, system variables; they cannot be deleted. CAS operates with the idea that everything that is not defined is considered symbolic. And if a variable is defined, then its value will always be substituted in first. So for example, if we store 1.25 into 'x', then 1+x is interpreted as 1.25. On the other hand, if 'x' is purged, then 1+x is interpreted as a formula 1+x.

3. Yes, it is. In fact, I would go as far as saying how variables (global, local, within apps, etc) could use an overhaul.

4. [Shift][( )][Backspace] (just get double ' and delete one of them)

5. I am sure there is some "logic" but any time I make an attempt to explain (even to myself) what I think is behind upper vs lower case, I end up finding too many exceptions. I think a large number of problems that arise are the result of a design choice: merging xcas with an HP38GII. The idea itself is fine; but each of those systems has ways of handling variables, command-line input, etc. that are often conflicting at times. Over time, this should be ironed out...

Edited: 23 Oct 2013, 2:43 p.m.