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Q.
The number of diagonals of a 18-sided polygon is_______
Geometry
Solution:
Given, number of sides $(n)=18$.
Number of diagonals of an $n$-sided polygon
$=\frac{n(n-3)}{2}, \text { where } n=18 $
$=\frac{18(18-3)}{2}=\frac{18(15)}{2}=135$