Question 427015
Parallel lines have the same slope m
perpnedicular lines have slope in the ratio of m1*m2=-1

IT MEANS YOU FIND THE RECIPROCAL OF M AND CHANGE THE SIGN
Let us see
line1 y=-3x+5   m1=-3
line 2 3x-y=8  or y=3x-8  m2=3  m1*m2=3*-3=-9
line is not perpendicular