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OpenStudy (anonymous):
How many diagonals are in a polygon with 18 sides
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OpenStudy (anonymous):
\[\frac{n(n-3)}{2}\]
OpenStudy (anonymous):
the formula is x(x-3)/2 so 18(18-3)/2 18(15)/2 9(15) 135 diagonals.
OpenStudy (anonymous):
135 diagonals
OpenStudy (anonymous):
\[\left(\begin{matrix}18 \\ 2\end{matrix}\right) - 18\] 135 diagonals.
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