Bring this point into the range equation, and then solve it to see if it is greater than 0 equal to 0 or less than 0.

Greater than zero is equal to zero on the outside and less than zero on the boundary.

You can get 1 equation by connecting two points, write the equation segment of each line, and then control whether it is greater than 0 or less than 0 by linear programming according to your diagram, so you can get several equations. If you draw them, that's the enclosed space you need.