is the line through points P(-8,10)and Q(-5,-12) perpendicular to the line through points R(9,-6) and S(17,-5)? Explain

Answer 1

PQ has slope (12-10)/(-5+8) = 2/3
RS has slope (-5+6)/(17-9) = 1/8
so the lines are not ⊥
why not?