The perpendicular line will have a slope of b/a.
To find this, we first have to solve our equation for slope intercept form.
ax + by = c ----> subtract ax
by = -ax + c ----> divide by b
y = -a/bx + c/b.
So we know the slope of this equation to be -a/b. Since perpendicular lines have opposite and reciprocal slopes, we know we can simply flip the fraction and make it a negative to get the new slope of b/a.
