How many triangles can be drawn all of whose vertices are vertices of a given n-gon and all of whose sides are diagonals ( not sides ) of the n-gon ? How many k-gons can be drawn in such a way ?
Number of triangles inside given n-gon?
4
$\begingroup$
combinatorics
discrete-mathematics
binomial-coefficients
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0See [this](http://math.stackexchange.com/questions/94425/) for a slightly related problem. – 2012-09-03