Plug in -2 for a, 3 for b, and -5 for c. Then it'd be | (-3)^2 - 2(-2)(-5) +5 (3) |. Then, multiply everything to get | 9 -20 +15 |. Then, add/subtract to get | 4 |. Finally, take the absolute value and get 4.
2) Constraints can be used to model different variables that cannot equal zero. They can be used in many different cases. For example, modeling money or a ball being dropped.