Question 112014
First find the slope through (9, 20) and (3, 2):



*[invoke slope 9, 20,3, 2]



Now to find the perpendicular slope, simply negate 3 to get -3. Now take the reciprocal of -3 (think of it as {{{-3/1}}}) to get {{{-1/3}}}


So the perpendicular slope to the line through (9, 20) and (3, 2) is {{{-1/3}}}