This PG code shows how to check student answers that are periodic.

PG problem file Explanation
DOCUMENT();
"PGstandard.pl",
"MathObjects.pl",
);
TEXT(beginproblem());


Initialization:

Context("Numeric");

$answer = Real("pi/2")->with(period=>pi);  Setup: This is self-explanatory. BEGIN_TEXT Enter a solution to $$\cos(\theta) = 0$$.$BR
$BR $$\theta =$$ \{ ans_rule(10) \} END_TEXT  Main Text: $showPartialCorrectAnswers = 1;