A man takes the shortest time when he swims perpendicular to the river velocity i.e., towards the north. Problem: A boat must get from point A to point B on the opposite bank of the river moving along a straight line AB that makes a 120-degree angle with the flow direction
In this article explained about different types of lines in geometry like straight line, curved line, Intersecting lines, Concurrent lines, Parallel Lines and transversal line with examples.
http://www.allmathtricks.com/types-of-lines/