@mmcdara 

Alternatively you could use the op command as a very rudimentary measure.

op(a)[1]
                   3

I'm sure it's just a typo but I think maybe you're missing a right side bracket.

((1+(y'(x))^2)^(-1)*1/y(x) ) = C

That aside it seems to work under maple 2020.  This is what I get ..

eq:= ((1+(y'(x))^2)^(-1)*1/y(x)) = C
                            
isolate(eq,y'(x))
                               
allvalues(%)
                                 

It works fine as you presented it. 

However the only way you get your answer is if Rc wasn't assigned a value.  If I change Rc:=Rc instead of Rc:=R2 as you wanted it then I get your "huh? what's that" answer.

Regarding copying everything into Mapleflow at once, I can't see at the moment but I will look into it.
***********edit update******* 
That seems to be a Mapleflow weakness, it's getting entered as a text container and can't be changed into an executable math container.  If I find a way I'll update this question but I'm stumped for now. 

Also this works.  Under Tools --> Options --> Display

Change Typesetting level from Extended to Maple Standard.  All your conversions in vector form can now be changed when you do the unit conversion.

add to your circle command to

circle(c,(x+4)^2+(y-3)^2=81,[x,y])

In Maple 2017 there is a debug icon.  If you click that, a new window should open with many options and you can click on quit.  You should end up back in Maple and can edit again. 

Maybe skip the ExcelTools Import and just use the plain Import - and import it as a Dataframe.

Is this what you mean?  int(f(x),x=a..b)  which is the same way to enter in Maple.  Or using the context menu on the left.

******edit added ***** additionally type int then press CTRL + spacebar  to bring up a list of options

You are using e as a variable Maple doesn't know you are trying to use it as a constant.

Change e^(-t) to exp(-t)

Press CTRL + R to add math in a text container.

Multiply value by Pi/180 to get radians.

Some prior Maple knowledge is helpful.  For your e  use exp(1), that will work.  Pi will work. 

For the speed of light and the gravational constants I think you'll have to define them.  They are available, but right now so far anyway, I can't figure out how to pull the constants out of Maple through MapleFlow - the long form way using GetValue doesn't appear to be working.

You can use rhs(ScientificConstants[GetConstant](c)[3]) in MapleFlow to pull out the value for c

You need to arrow right after typing units to get out of the units.

5 crtl+shift+u ft (right arrow) + etc.....

This is where I believe your issue is. 

**edit added** I had a quick look in the user manual, and that minor detail to arrow out of the units was not mentioned, but it's similar to getting out of an exponent or denominator so just a minor miss as it was probably implied.

So initially I thought it would automatically assign to the first units mentioned in the equation, but that doesn't matter.  It seems to be preset to standard SI units. 

It would be nice to have a list of preset preferences the worksheet would work as.  (ie units settings and digits - it would be nice to have a preset number of decimal places shown.  3 decimal places I think was chosen as a happy medium.  However for example - the smallest medium of measure for carpentry is 1/16" which is 0.0625 ( I mean mostly - there are some tape measures out there with 1/32" scales - good for machining, milling or lathe work I guess ultimately at that point you're working with micrometers and calipers which are likely digital).  If it was going to be a set value personally I would have gone with 4 decimal places but ultimately I would let the user choose in a user preferences. 

For MapleFlow2022 the digits option is still only individually chageable by the context panel on the right side.

Optionally wthout using the context menu there is a workaround using the convert string option, you can display the number of decimal places as set in Digits.  Of course this is just an adhoc measure. 

Variable re-assignment works in MapleFlow 2022.