Science:Math Exam Resources/Courses/MATH200/December 2012/Question 04/Hint 2

To handle the boundary case, break up the boundary into 4 cases: $x=-1$, $x=3$, $y=-1$, and $y=1$. For the first line, you get a new function $g(y)=f(-1,y)$, which you can then optimize subject to the constraint $-1\le y\le 1$. The other lines are similar.