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min and max no of parts that are angles so that n lines divide the plane

Source: 2011 Sharygin Geometry Olympiad Correspondence Round P18

April 6, 2019
geometrycombinatorial geometrylinesDissecting planeSharygin Geometry Olympiad

Problem Statement

On the plane, given are nn lines in general position, i.e. any two of them aren’t parallel and any three of them don’t concur. These lines divide the plane into several parts. What is a) the minimal, b) the maximal number of these parts that can be angles?