Straight Lines and Slope The slope of a line, m, is a rate of change which is constant in linear equations.When a line passes through the points (x1, y1) and (x2, y2), the slope, m, is expressed:Slopes may be positive, negative, zero, or undefined(does not exist).Positive Slope Lines that have positive slope, rise from the lower left to the upper right on the … [Read more...] about Straight Lines and Slope