## WeBWorK Problems

by Sean Fitzpatrick -
Number of replies: 5

I've been looking for an example or documentation on how to have a quesiton where the answer is a vector with variable entries, but so far I haven't been successful.

The context in my case is linear transformations. I want students to find a formula for a linear transformation from R2 to R2, and I want to format the problem like T(x,y) = __________________

rather than T(x,y) = (_____x + _____y, _____x + _____y)

and have students enter an answer like (3x+2y, -x+4y). The vector math object doesn't seem to like entries that are formulas.

### Re: Vector answer with variables

by Sean Fitzpatrick -

I tried to do something like the following:

$ans1 = Formula(2*x+3*y);$ans2 = Formula(-4*x+5*y);
$ans = Vector($ans1,$ans1); This gives me the error message: Can't locate object method "weaken" via package "main" at [PG]/lib/Parser/List.pm line 67 from within main::Vector In reply to Sean Fitzpatrick ### Re: Vector answer with variables by Glenn Rice - You will need to use the Vector context. Note that the variable "y" is already in the Vector context, so there will be no need to add that. Also, you need to quotes on the Formula arguments. It should be Context('Vector');$ans1 = Formula('2x + 3y');
$ans2 = Formula('-4x + 5y');$ans = Vector($ans1,$ans2);

### Re: Vector answer with variables

by Sean Fitzpatrick -
Thanks. That works. The only remaining issue is that students have to use angle brackets to enter their answer, rather than parentheses.
Not ideal, but I can add an instruction.

### Re: Vector answer with variables

by Alex Jordan -

You can direct the context to parse parentheses as vector delimiters. Look up the wiki doc on modifying contexts, parens section.