Find the slope of any line perpendicular to 
the line through point (6,3)and (7,7).

You need two things:

1. The slope formula
2. The fact that perpendicular lines have slopes
   which are reciprocals but with the opposite sign.



1. 
     y2 - y1     (7) - (3)     4
m = --------- = ----------- = --- = 4
     x2 - x1     (7) - (6)     1

2.

The slope of a line perpendicular to a line with 
slope 4/1 is the reciprocal of 4/1 with the sign
changed.  That is, it's

        m = -1/4

Edwin