Number of diagonals in a polygon with n sides is n*(n-3)/2 A pentadecagon has 15 sides, so n = 15
Number of diags = 15*12/2 = 90
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It has 40 diagonals.Improved Answer:-Using the formula for diagonals of a polygon: 0.5*(442-132) = 902 diagonals
There are 275 diagonals in a shape with 25 sides. The formula is n*(n-3)/2
It must have 19 sides to comply with the formula:- 0.5*(192-(3*19)) = 152 diagonals
Using the formula 0.5(n^2 -3n) whereas n is number of sides, altogether there are 104 diagonals in a 16 sided polygon
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