Calculate the slope of line segment AB as m₁. [tex]m_{1} = \frac{4-1}{p-6}= \frac{3}{p-6} [/tex]
Calculate the slope of line segment BC as m₂. [tex]m_{2} = \frac{q-1}{9-6} = \frac{q-1}{3} [/tex]
The product of the slopes of perpendicular lines is equal to -1. Therefore [tex]( \frac{3}{p-6})( \frac{q-1}{3})=-1 \\\\ \frac{q-1}{p-6}=-1 \\\\ q-1 = 6-q \\\\ p+q = 7 [/tex]
