For reference lets call the "upper" line that crosses the Y-axis at
and the "lower" line that crosses the Y-axis at
For Line A
We note the following points are on the line:
Since this is a straight line, the slope is constant for all pairs of points:
The identified area is below this line and the hollow "bubbles" indicate the points on the line are not to be included.
Therefore Line A provides the constraint
For Line B
The V shape of Line B indicates that the equation for this line involves the absolute value of a linear expression of
Since the "turning point" occurs at
the absolute expression is
Since the "turning point" is at
we note that relative to
that is the equation for Line B
The identified area is above (and includes, since there are no "bubbles") Line B.
Therefore Line B provides the constraint
Combining the Areas
The identified area meets both Line A and Line B constraints.
Therefore the identified area is constrained by
or (in set notation)