# Plus/Minus Operator

It is possible to perform computations with the operator, as explained here. Therefore, the student is allowed to use the symbol too. Recall that the result of the operator is a list (not a set!).

Let us start with an easy example: solve the equation . We simply write as correct answer

As we already mentioned, it is interpreted as a list: ; this means that the order matters and both options are enclosed in braces. Therefore, we have to change the default settings to allow the students to answer with any correct syntax:

• Braces are not necessary: Input options > Input syntax > Lists without enclosers
• The order is not important: Validation options > Comparison with student answer > Compare as sets

Finally, we can test the behavior.

A well-known expression is a formula for solving the second-order degree polynomial. For instance, the roots of the polynomial are given by . Let us ask the student to write this expression.