I'm trying to write a problem on the subject of related rates in differential calculus, and I'd really like to have the capability of having students' answers involve primes. That is, if we have something like A(t) = x(t)+y(t), ask what is A'(t), and the students' answer should be x'(t) + y'(t). I know there are ways of getting around this by stating x'(t) = some constant, and y'(t) = some other constant, but I believe we have the capability of using 'prime' notation.
I found
parserFunctionPrime.pl, which seems to be designed for this sort of use, but something goes wrong when it comes to comparing students' answers.
So here is what I tried: I want to ask, if A(t) = pi [r(t)]^2, what is A'(t) in terms of r(t) and r'(t)? The answer should just be the derivative with respect to t, A'(t) = 2 pi r(t) r'(t)
I defined t as a new variable, declared r(t) as a function of t(whose actual definition doesn't matter, I think in this case?) and set $dr = r'(t) ;
As far as I can tell, this is exactly what I am supposed to do , according to the documentation in the link above. Then when I compute these into a formula and use it as the answer, it still seems to work, until I actually compare an answer with it.
Attached is a screencap of what happens when I try to enter the correct answer.
If you look at my code in the post above, you'll notice I've commented out the disable line at the bottom, because when I leave it there, I have this error:
Any help on this would be appreciated.
Entered  Answer Preview  Correct  Result  Messages 

2 pi r(t) r'(t)    incorrect  Unexpected character '''
