Question 678242
The slopes of perpendicular lines are opposite reciprocal of each other: {{{m[1]=-(1/m[2])}}}

So you need to re-write your line equations in a form that gives you the slope. I will use slope-intercept form:

{{{ax+y=c}}} becomes {{{y=-ax+c}}} with {{{m[1] = -a}}}

{{{x-by=d}}} becomes {{{y=(1/b)x-d/b}}} with {{{m[2] = 1/b}}}

Replacing {{{m[1]}}} and {{{m[2]}}} into the relation between slopes of perpendicular lines:

{{{-a = -b}}}

Thus

{{{b=a}}}