Asked by Lily

The coordinates of the endpoints of ab and cd are A(x1, y1), B(x2, y2), C(x3, y3), and D(x4, y4). Which condition proves that ab//cd ?
Answered by oobleck
If by // you mean parallel ║ then the slopes must be the same:
(y2-y1)/(x2-x1) = (y4-y3)/(x4-x3)