What is uses of shadow graph?

Answer 1

I will guess that what you refer to as a "shadow graph" serves as a way to visually represent all the answers, or solutions, to a linear inequality. For instance, if you graph y=x (a linear equality), you get the diagonal line through the origin heading 45 degrees up and to the right in one direction and down and to the left in the other. Any point on that line is a solution, even extended beyond the visible graph in both directions, "forever". However, if you graph yno point on the line is part of the solution, but any point in the shaded area (or outside the visible graph below and/or to the right of that shaded area) is a solution. The diagonal line would have been solid if y was less than or equal to x, which would include the line itself as part of the solution set.