** Using WeBWorK **

In the following problem the student gets the message "Your union can be simplified by combining some sets" if he enters the wrong answer "(-inf,-3) U (1,inf)". In my opinion this is misleading, because it suggests that the answer is right but could be further reduced. Neither of it is the case.


DOCUMENT();
loadMacros(
"PGstandard.pl",
"PGML.pl",
"MathObjects.pl",
"PG.pl",
"PGbasicmacros.pl",
"PGanswermacros.pl",
"PGcourse.pl",
);

TEXT(beginproblem());

Context("Interval");

$I1 = Interval("(-infinity,-3)");
$I2 = Interval("(1,infinity)");
$I1intI2 = $I1->intersect($I2);

BEGIN_PGML

This problem will produce the error message 'Your union can be simplified by combining some sets' when the wrong answer "(-inf,3) U (1,inf)" is entered.

Determine the set of all [``x \in \mathbb{R}``] that fulfill the condition [``x < -3 \text{ and } x > 1``]: [_______________]{"$I1intI2"}.

END_PGML

ENDDOCUMENT();