Given y = mx+b, b is always equal to the y intercept, because b is the value of y when x = 0.

m is always slope, because a change of +1 in the value of x yields a change of +m in the value of y. Since slope = rise over run, this results in slope equal to m/1, or m. For a more formal explanation, consider two different values of x:

[ and

. Plug those into the equation y = mx+b and we get:

where (x1,y1) and (x2, y2) are two different points on the line. The slope of the line is the "rise over run" calculated as the change in the y-value divided by the change in the x-value:

slope = (change in y)/(change in x)

slope =