Question

4) Calcular o número de diagonais de um pentadecágono.
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Answer 1

d = n(n-3)/2 = 15(12)/2 = 90 ✓

Answer 2

$\sf d=\dfrac{n(n-3)}{2}$

$\sf d=\dfrac{15(15-3)}{2}$

$\sf d=\dfrac{15(12)}{2}$

$\sf d=\dfrac{180}{2}$

$\boxed{\boxed{\sf d=90}}$