50g

Hello, all. I am an AP Calculus teacher with many years experience
using the 48G. Now trying to make the transition to the 50G and some
things don't work the same way.

For instance, on the 48, you can define N(x)= x-F(x)/F'(x), define F
(x), say x^3-7, enter a numeric value, press N on the var list, and
after eval, have a second iteration of the approximate root of F(x)
near x. So, the N(x) recognizes x, F(x) and F'(x).

When the same strategy is used on the 50, I always get an answer of
infinity. Either the N function doesn't recognize the F or the
derivative is made equal to zero. Any ideas?

Secondly, I have tried many different ways to graph f(x)=x^(odd
fractional power), for instance x^(5/3). It seems crazy, but the only
way I can get the 50 to give the entire graph is to let F(x) = x^2/ x
(1/3). This is truly pathetic and I hope someone knows a more elegant
solution. Thanks in advance for all help!

Hello there, what is happening with your equations is that the F(x) in N
(x) is different from the F(x) you define, for example when you define f
(x)=x^3-7 the calculator creates a program that looks like this:
<< ¨ x 'x^3-7' >>
and stores it in a global variable called 'F'; this means that in run-
time the calculator create a temporary local variable called 'x' this
variable is different that a global variable called 'x' that you may
have in your current directory. The same is true for the F(x) you
define and F(x) in N(x). A better approach is to have a program N like
this:
<< ¨ x0
<< 'x' DUP F DUP 'x' Ý / - 'x' x0 = SUBST ¨NUM >>

>>

I hope this helps.

--- In 50g@yahoogroups.com, "Juan C." <jcbuchin@...> wrote:

>
> Hello there, what is happening with your equations is that the F

(x) in N

> (x) is different from the F(x) you define, for example when you

define f

> (x)=x^3-7 the calculator creates a program that looks like this:
> << ¨ x 'x^3-7' >>
> and stores it in a global variable called 'F'; this means that in

run-

> time the calculator create a temporary local variable called 'x'

this

> variable is different that a global variable called 'x' that you

may

> have in your current directory. The same is true for the F(x) you
> define and F(x) in N(x). A better approach is to have a program N

like

> this:
> << ¨ x0
> << 'x' DUP F DUP 'x' Ý / - 'x' x0 = SUBST ¨NUM >>
> >>
> I hope this helps.
>

Thank you very much! I wondered if global/local variable would be
the reason, but I didn't know what to do about it. Any thoughts on
the odd fractional root graphs? Thanks again!

First of all, I am sorry the symbols I put before didn't show up in the
replay I posted, so here it goes again ("->" means the arrow and "d" is
the differential:
what is happening with your equations is that the F(x) in N(x)
is different from the F(x) you define, for example when you define f
(x)=x^3-7 the calculator creates a program that looks like this:
<< ->¨ x 'x^3-7' >>
and stores it in a global variable called 'F'; this means that in run-
time the calculator create a temporary local variable called 'x' this
variable is different that a global variable called 'x' that you may
have in your current directory. The same is true for the F(x) you
define and F(x) in N(x). A better approach is to have a program N like
this:
<< -> x0
<< 'x' DUP F DUP 'x' d / - 'x' x0 = SUBST ->NUM >>

>>

For the second question I have no clue, nothing seems to work, I am
posting your question in hp forums, I hope they have an answer.

 

Hello there, I posted your second question in hp forums, and there is not an easy solution to that problem. Giancarlo Mattioni suggested this:

" If you don't mind, I'd point you to a comp.sys.hp48 thread (not that recent...):

http://groups.google.com/group/comp.sys.hp48/browse_frm/thread/375e156699e66

951/ebc3964b576b5bc1?hl=it&lnk=gst&q=whole+graph#ebc3964b576b5bc1

 

 

In summary, the "other half" of the graph can't be showed as it is "made of" complex values for negative x values.

I think you can catch the picture you want if you try to graph:

Y1(X)=|X^(5/3)|  "

So I tried the IFTE function like this: IFTE(X>0,X^(5/3),-ABS(X^(5/3))), it isn't an elegant solution but it works.

--- In 50g@yahoogroups.com, "Juan C." <jcbuchin@...> wrote:

>
>
>
> Hello there, I posted your second question in hp forums, and there

is

> not an easy solution to that problem. Giancarlo Mattioni suggested

this:

>
> " If you don't mind, I'd point you to a comp.sys.hp48 thread (not

that

> recent...):
>
>
>
>
>

http://groups.google.com/group/comp.sys.hp48/browse_frm/thread/375e15
669\

> 9e66
>
> 951/ebc3964b576b5bc1?hl=it&lnk=gst&q=whole+graph#ebc3964b576b5bc1
>
>
>
>
>
>

<http://groups.google.com/group/comp.sys.hp48/browse_frm/thread/375e1
566\

> 99e66951/ebc3964b576b5bc1?

hl=it&lnk=gst&q=whole+graph#ebc3964b576b5bc1>

>
> In summary, the "other half" of the graph can't be showed as it

is "made

> of" complex values for negative x values.
>
>
>
>
> I think you can catch the picture you want if you try to graph:
>
> Y1(X)=|X^(5/3)| "
>
>
> Thanks again. Much appreciated!
>
> So I tried the IFTE function like this: IFTE(X>0,X^(5/3),-ABS(X^

(5/3))),

> it isn't an elegant solution but it works.
>