The graph for x = 5 is:

Three ordered pairs that satisfy the equation (point from the graph) are:

(-1, 5),(5, 0) and (5, 1)

The slope of a line is given by:

m = (y2 - y1)/(x2 - x1) where (x1, y1) and (x2, y2) are points from the graph.

If you take two points from the graph, the x values will always be the same.

Therefore, you will be dividing by 0, and the slope is undefined.