Parallel lines are indicated by arrows going in the same direction. Parallel lines are indicated by arrows going in the same direction. If there is more than one set of parallel lines in a diagram, ...

Horizontal lines run left to right, parallel to the horizon, with slope 0 and equation y = k. Vertical lines run top to bottom, perpendicular to the horizon, with undefined slope and equation x = k.

Whether you are sketching graphs in mathematics, understanding directions in geography, or reading blueprints in design class, horizontal and vertical lines are concepts you cannot avoid. They form ...