how do you find a line perpendicular to another if the given line is in standard form, Ax+By=c?

Question

also, i need some help finding a line perpendicular to y=3 and crosses the points (2,4). help plz?

Answer 1

Your first line can be rewritten
y = -(A/B)x + C/B
Its slope is -A/B

Any line with a slope B/A will be perpendicular to your first line.
One form would be Bx -Ay = d
where d is any constant.