## WeBWorK Problems

### Checking against multiple correct answers

by Danny Glin -
Number of replies: 1
I was wondering if there was an easy way to specify a short list of different correct answers for a single answer blank. The problem is as follows:
Students are asked to calculate the characteristic polynomial of a 3x3 matrix. Depending on how they are taught, some will answer det(A-xI) and some will answer det(xI-A), which differ by a factor of -1. I would like the system to accept either of these two answers, but nothing else.
Any suggestions?
    $p = Formula("your formula here"); ... ANS($p->cmp(checker => sub {
my ($correct,$student) = @_;
return $correct ==$student || $correct == -$student;