When the slope is positive, it means that as we view the graph of the line from left to right, as x increases, so does y. We write m > 0

When the slope is negative, it means that as we view the graph of the line from left to right, as x increases y decreases . We write m < 0

When the line has zero slope, we have a horizontal line. We write y = n, where n is a constant, and say that m = 0 