From: Marielouise (for Teacher2Teacher Service)
Date: Jul 12, 1998 at 15:49:30
Subject: Re: Reason for using "m" and "b" in y=mx+b

Michelle, 

You have asked an age old question: "Why is m used to denote the
slope?"  Math historians do not know.  Traditionally there is an answer 
given for the use of "b" for the y-intercept. 

When graphing in three space: (a,0,0) is the point where the x-axis 
intersects the line or plane; (0,b,0) is the point where the y-axis 
intersects and (0,0,c) is the point where the z-axis intersects. The value 
of "b" is then the value on the y-axis or the y- intercept.  Similarly "a" 
and "c" are the x-intercept and the z-intercept.  In two dimensional space 
there are only two axes and two possible intercepts.

Have you ever considered the two intercept form of a line?  It is

                            (x/a) + (y/b) = 1,

where a and b are the x-intercept and y-intercept.

 -Marielouise, for the Teacher2Teacher service