Which of the following expressions is incorrect?

|-12| = 12
-|-12| = -12
-|12| = 12
|12| = 12

The incorrect expression is -I12I=12 (3rd one). This would actually equal -12. In this case, the absolute value of a positive 12 would just equal positive 12. The negative sign on the outside of the absolute value would distribute over after doing the absolute value, therefore making the number a -12. 

Hope this helps :)