ax + by = c
by = -ax + c
y = (-a/b)x + c/b......the slope here is -a/b. A perpendicular line will have a negative reciprocal slope. To find the negative reciprocal, we flip the slope and change the sign. So we have a slope of -a/b.....flip it and it becomes -b/a....change the sign and it becomes b/a.....so ur perpendicular line will have a slope of b/a <==
