They aren't, they're parallel.
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When the perpendicular lines are horizontal and vertical.
It is a vertical line touching a horizontal line
perpendicular lines
Perpendicular
Examples of horizontal lines in the real world include the horizon where the sky meets the land or sea, the straight line of a calm lake's surface, the boundary between the wall and floor in a room, and the straight line of a ruler placed flat on a table. Horizontal lines are parallel to the horizon and perpendicular to vertical lines.