If A(x1, y1), B(x2, y2), C(x3, y3), and D(x4, y4) form two line segments, AB and CD , which condition needs to be met to prove AB is perpendicular to CD ?

Question

If A(x1, y1), B(x2, y2), C(x3, y3), and D(x4, y4) form two line segments, AB  and  CD , which condition needs to be met to prove  AB is perpendicular to CD     ?

loser66 · Answer

AB=?
CD=?

anonymous · Answer

A(x1, y1), B(x2, y2), C(x3, y3), and D(x4, y4)

loser66 · Answer

nope, I ask AB , not A, B

anonymous · Answer

doesn't tell you

loser66 · Answer

hahaha... keep it in secret?? ok, so, I don't know what AB and CD are. How can I help you to solve it?

loser66 · Answer

if the problem doesn't tell you, you have to find them out.

anonymous · Answer

i dont know how to solve this problem

loser66 · Answer

Ok, 
AB = (x2-x1, y2-y1)
CD=? your turn

anonymous · Answer

well then how

loser66 · Answer

answer me first, what is CD