@John Fredsted 
I tried this code, it didn't work. I got
f := (x,y) -> x + y;
f([2,0],[3,4]);

output: [5, 4]

@Ronan He has a negative in his square root .

https://snipboard.io/CzjiFa.jpg https://snipboard.io/CzjiFa.jpg https://snipboard.io/CzjiFa.jpg https://snipboard.io/CzjiFa.jpg https://snipboard.io/CzjiFa.jpg https://snipboard.io/CzjiFa.jpg

@Carl Love 
I did post this question before.
https://www.mapleprimes.com/questions/230885-Maple-Help-Only-Works-Once-Per-Session

It was never answered satisfactorily, also if i try to repost it I get a warning
please don't duplicate. That means I have to delete the question?

@tomleslie 
Speaking of bugs and maple 2020... when I press F1 help multiple times, it stops working.
When use the maple command  ?<command>, it works only one time. Then won't open help again

I see the NULL command in one of your lines. I wonder what it does. This is an amazing code.

Specifically i would love to understand this line
C := coeffs(f(x, y), v, M); seq(`if`(member(op(i, [M]), N, 'j'), op(j, V) = op(i, [C]), NULL), i = 1 .. nops([M]));

@Joe Riel 

I am curious, why does 
" map(`+`, 3, L) "   output  "3 + [1,2,3]" ,  but  " map(`+`, L, 3) " outputs " [4,5,6] ".

On the other hand `*` displays commutativity in the arguments:
i.e.  "map(`*`, 3, L) "  and  " map(`*`, L,3) "  both output  " [3,6,9]"

@acer  I am using windows 10 pro, version 2004. Maple is release 2020.1

Below are some screenshots.

@dharr log10() is a useful command. Does not seem work with other bases, e.g. log2(8) .

@acer Sorry about that. Should I delete this post and repost a new one so that it appears on the right side where it says 'recent questions', or is this considered against etiquette.

@ecterrab Thanks for the file. It worked.

@John Fredsted 

is it possible to improve the code so it posts positive coefficients

expMod(2*x^21 - 3*x^7 + 10*x^3 - 18,17);

to output 14*x^7 + 2*x^4 + 10*x^3 +16

@nm sin^(3) (x) seems like bad notation, since we reserve f ^(n) for the n'th derivative of a function

@Rouben Rostamian  

instantaneous might be stretching it , but it takes about a second

@acer Thanks. And I like how you answered it in two different ways. I feel stupid, I must have missed some key info in the help page.

@rlopez

I checked the student calculus 1 package, it does not have second derivative test.

But I found it with this command:

with(Student[MultivariateCalculus]);

This is a very useful package.
Thanks i will use this in the future.