Find the number of diagonals that can be drawn in an n-side polygon

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  • #1
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Find the number of diagonals that can be drawn in an n-side polygon.

The answer is n(n-3)/2.

I don't know how to do that.
 

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  • #2
Tide
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Set up a recursion for the number of diagonals in an n-gon: [itex]D_{n+1} = D_n + n - 2[/itex].
 
  • #3
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I don't understand how can I set up
[itex]D_{n+1} = D_n + n - 2[/itex].
 
  • #4
HallsofIvy
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How many diagonals can be drawn from 1 vertex? If you multiply that by the number of vertices you will get the wrong answer! Do you see why? How can you fix it?
 

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