$c = 2; Compute("x^(3*$c)");you would get the equivalent of

Compute("x^6");This avoids your having to make separate variables for computed values within a formula.

This is good except in the situations where you really want to leave a constant in a symbolic rather than numeric form, as in your case. To handle that, MathObjects have two flags that control the reduction of constant values. So if you do

Context("Numeric"); Context->flags->set( reduceConstants => 0, reduceConstantFunctions => 0, );before you call

`Compute()`

, that will preserve the original symbolic form in the `{original_formula}`

value. E.g.,
$ans = Compute("2/sqrt(3)");would have

`$ans->{original_formula}`

as 2/sqrt(3) rather than 1.1547.
I noticed a couple of other items in your code. First, you note that

$ans = List(Compute("$y")); ... $sol = $ans->{original_formula}makes

`$sol`

be nothing. This is because there IS no original formula in this case, since you are calling `List()`

directly on another MathObject (the result of the `Compute()`

call. So no formula is parsed to do this. Only `Compute()`

produces `{original_formula}`

. (Of course, the element *contained*in the list has a

`{origin_formula}`

, so you could use `($ans->value)[0]->{original_formula}`

to get it.)
Second, you don't need to put `$y`

in quotes, since it is already a string. This is redundant. You can just do

$ans = Compute($y);

Third, you have set the tolerance to 0.0000000000001, which is very close to the limits of internal representations used by WeBWorK. (The numbers stored internally have 16 to 17 significant digits, and you are asking for 14 of those to be correct, but round-off errors and other numeric instability can easily affect the 13th digit.)

I suspect you are trying to force the answer to be given as a formula involving `pi`

and square roots rather than as a decimal, but I would recommend using one of the means of preventing the student from entering a decimal explicitly rather than trying to require this kind of excessive precision. Try adding

Parser::Number::NoDecimals;after selecting the context.

Finally, since you are looking for symbolic answers, you might want to show the student's answer that way as well. So you might want to use

Context()->flags->set(formatStudentAnswer => "parsed");so that the student answer isn't reduced.

Hope that helps.

Davide