Parallel lines have the same gradient, so use the given coordinates to find the gradients of the lines.
Perpendicular lines have gradients that multiply to give -1. So use the given coordinates to find the gradient, and multiply them.
Perpendicular lines can be found on the globe, where longitudinal and latitude lines intersect. It's important for them to be perpendicular as they are used to measure time and location through geographical coordinates, and since Earth is essentially a sphere with 360 degrees, the lines have to be perpendicular for measurement.
(I could be wrong!!! I found some answers online and implemented them here.)
