Question

Qual o número total de Diagonais de um Octógono Regular?

(__)20

(__)24

(__)28

(__)32​

Answer 1

$\large\displaystyle\boxed{\begin{array}{l} \rm{d = \dfrac{n \cdot(n - 3)}{2} \rightarrow \begin{cases} \rm \: d = diagonais \\ \rm \: n = n\acute{u}mero\,de\,lados \end{cases} } \\ \rm{d = \dfrac{8 \cdot(8 - 3)}{2} } \\ \\ \rm{d = \dfrac{8 \cdot5}{2} } \\ \\ \rm{d = \dfrac{40}{2} } \\ \\ \boxed{ \boxed{ \rm{d = 20}}} \checkmark\end{array}}$