Internet Resources for the Calculus Student

The Slope of a Line

 
The slope of a straight line is defined in terms of any two points on the line as the ratio (rise)/(run), or in Cartesian coordinates (change in y)divided by (change in x) .   This measures in some sense how fast the line rises as we move along it.  For a horizontal line (parallel to the x-axis in Cartesian coordinates) the slope is zero since y does not change (ie rise=0), and for a vertical line the slope is undefined (since x does not change so "run"=0). For more detail on this and other related issues you might want to look for material on Linear Functions.