Slope of a Line

In the equation of a line in the plane y = kx + b (seeANALYTIC GEOMETRY), the coefficient k is called the slope of the line. The slope characterizes the inclination of the line relative to the x-axis. In a rectangular coordinate system the slope k = tan φ, where φ is the angle the line makes with the positive x-axis, the angle being measured counterclockwise.