Consider the equation x + y = 5. It passes through the points (0, 5) and (5, 0). The line x + y = 5 is represented by AB. Consider the inequality x + y < 5. Put x = 0, y = 0 0 + 0 = 0 < 5, which is true. So, the origin O lies in the plane x + y < 5 ∴ Shaded region represents the inequality x + y < 5.