@Preben Alsholm 

Thanks

I will study it again

Interesting question, because i quess there must be always a numerical solution to a ODE ?
I do see also there are certain conditions about Existence and Uniqueness of a ODE
Seems to me if there exists a closed (analytical ) solution of a ODE, then a numerical solution exitss too. 

@acer 

 "So, the version you cited didn't even produce the claimed output in the saved versions of those accompanying worksheets."

---------------------------------------------------------------------------------------

In Document mode, the reader should use the Exploration assistant for Interactive
Exploration.
Procedures. Declare local variables within procedures.
> # Program 1: Procedures.
> # The norm of a 3-dimensional vector.
> norm3d:=proc() local a,b,c;sqrt(aˆ2+bˆ2+cˆ2) end;
> norm3d(3,4,5);
5
√
(2)

Its from the pdf : dynamical systems with applications using Maple -second edition , page 9 (0.4. Simple Maple Programs)

Also included worksheet does not show the right code.

@Kitonum 

Thanks!

Finally knowing know how it works 
The example of the arithmetic mean of a sequence of numbers for any number of these numbers is astonishing
Don't know how it is constructed with a + and so on

Thinking on a standard formula for this:  arithmetic mean of a sequence of numbers for any number of these number

@acer 

Thanks

Yes, this example is from a short tutorial in studying dynamical systems.

" Upload and attach your worksheet. (Why do you need to be asked this?)

[edit] If this is some claim you found online or in a text, why not share the source of that with us?"

Next time  when this occur again a question i post it in maple example as a worksheet. 
Of course i do want share source text, but it was late yesterday evening when i read the maple primes  e-mail.
 Went  biking that day and we are here now in a tropical temperatures week( unique ) in Holland and was a little bit exhausted.
The next morning then..
  

@nm 

Thanks

It gives me the same result as yours code showed, so no need to contact Maple support.
Its old code and worked on earlier maple versions then?

I was too thinking on a returm, but this code looks strange without end proc and no ; for the statement

Also you defined input parameters too, so i don't know what the author of this code has in mind for this as a (confusing) example ?      

@acer 

Thanks

Because it was not working this procedure  and from this a long unsolved issue that  i never understood the use of a proc ( ) without a parameter definition

@vv 

Thanks

It works again

@nm 

Thanks

Seems to be now working with a new restart of Maple after two times of opening in Maple earlier with a error message like in my posted example  ?
It are old worksheets and get a overhaul in Maple and i thought that it was the cause of not plotting.

Its working now correct and see the integral curves  in the DEplot 

@Carl Love 
Thanks

Remarkable that all answers/results in Maple not automated can be checked
There is a human involved to sort this out with limitations also too as i understand it correct.

@acer 

Interesting, but al that do and don't  makes it not really easy.
Is it not possible in a "next level" of programming to simplify this ? 
In general ask myself can Maple be programmed to a higher level of user-friendlyness ?

Its a Achimedean Solid this regular tetrahedron ?
For someone who wants to learn the geom3d  package better  its a useful example 

See also https://www.mapleprimes.com/questions/230162-Calculating-Area-Of-Shadow-#answer271424

ode:=diff(f(x),x)=f(x)^(-1);
dsolve(ode);
                                   d          1  
                           ode := --- f(x) = ----
                                   dx        f(x)
                                (1/2)                     (1/2)
              f(x) = (2 x + _C1)     , f(x) = -(2 x + _C1)     

@janhardo 

@Carl Love 

Thanks

Well , i don't see it , thats why i could not figured out by meself

@nm 

Thanks

You are right for this type of ODE its solved by integrating and rather easy to solve.