90.
Number of diagonals = number_of_sides × (number_of_sides - 3) ÷ 2
→ For a Pentadecagon which has 15 sides:
Number of diagonals = 15 × (15 - 3) ÷2 = 15 × 12 ÷ 2 = 90
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A Pentadecagon had 15 sides
9 diagonals
Two.Two.Two.Two.
None
How many diagonal lines does a 1million sided shape have