Hi all,

On the advice of the kind respodents on this thread, I have installed the STACK question type to create questions that require students to reason algebraically. One of the questions is to give the time derivative of an expression.

The expresion is : [l1*sin(theta(t)), -l1*cos(theta(t)),0] (which is the position of a point mass at a distance l1 from the origin, under an angle of theta(t) with the negative y-axis).

I sucessfully differentiated this in the STACK question editor, the quiz attempt review shows that the answer is supposed to be:

Which is correct, but now I would like the student to be able to answer that, since we do not want to provide a value or function for theta, but we do explicitly want it to depend on t. In the student review, the suggested way to type the answer is given as:

[l1*cos(theta(t))*'diff(theta(t),t,1),l1*sin(theta(t))*'diff(theta(t),t,1),0]

However, this is not allowed, since "Apostrophes are not permitted in responses" (as far as I know this is not something I prohibited). Leaving out the two apostrophes is interpreted as:

Which is neither the correct answer, nor an appropriate way to display the first derivative. Using diff on the original position vector in the students response does not work either (nor would it be educative).

My first question: is this in any way solvable?

My current workaround is by defining the first derivative of theta(t) as phi(t). Though this is not desirable, the idea is similar to the default course notation, where:

This workaround works fine, though it does not allow the ease of using diff in the question editor (my task is to create the concept for testing, but at some point the responsible lecturers and their student assistants should be able to create questions). Furthermore the workaround deviates too much from the course notation.

My questions are:

Is there a way to overcome the first problem, i.e. allow students to enter the derivative of theta(t) with respect to t (ans also without allowing students to use diff on the whole equation)?

Is there a way to use the symbol $\dot{\theta}\(t\)$ (to replace the work-around using $\phi\(t\)$)?

Is there a way to combine the ease of the teacher using diff that allows the resulting d/dt $\theta$ (t) to be equal to $\phi$(t)?

I am using Moodle version 3.5 (as a standalone Windows version for testing, but likely on a version 3.5 moodle on a server once it is deployed) and STACK version 4.2.1 for Moodle 3.0+ (2018080600)

Many thanks in advance,

With kind regards,

Yorick