posted by erin .
evaluate:-[a-3b],if a= -2 and b= 6
20 correct? these are absolute bars by the way.
No, not correct. |-20| is 20. Put a minus sign in front of it and you have -20. The error is made going from line 2 to line 3.
but absolute is never negative
There is a minus sign OUTSIDE of the absolute value signs. It reverses the sign of the absolute value term, making it negative.
an absolute value can never be negative