Brain Teasers
Diagonals of a Dodecagon
Jim and Tom play a game.
A dodecagon (i.e., a 12-sided polygon) is drawn on a piece of paper. They take turns drawing diagonals, i.e., a line segment to connect two non-adjacent vertices. However, they are not allowed to draw a diagonal that intersects another diagonal already drawn.
If a player can't draw another diagonal, he loses and his opponent wins. Jim draws first and Tom draws second. What's the correct strategy for Jim to win?
A dodecagon (i.e., a 12-sided polygon) is drawn on a piece of paper. They take turns drawing diagonals, i.e., a line segment to connect two non-adjacent vertices. However, they are not allowed to draw a diagonal that intersects another diagonal already drawn.
If a player can't draw another diagonal, he loses and his opponent wins. Jim draws first and Tom draws second. What's the correct strategy for Jim to win?
Hint
If you think that the correct strategy is for Jim to first draw a "longest diagonal", which divides the dodecagon into two halves, then mimic Tom's moves, you're tricked.Answer
If a player wins, then the dodecagon must have been divided into triangles, which requires EXACTLY NINE cuts.Therefore, Jim ALWAYS wins no matter what strategy he uses!
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