Question

Qual é o número total de diagonais de um octógono convexo?

Answer 1

$d= \frac{n.(n-3)}{2}$

$d= \frac{8.(8-3)}{2} = \frac{8.5}{2} =4.5=20$

Answer 2

$\large\boxed{\begin{array}{l} \rm \: d = \dfrac{n \: . \: (n - 3)}{2} \\ \\ \rm \: d = \dfrac{8 \: . \:(8 - 3) }{2} \\ \\ \rm \: d = \dfrac{8 \: . \: 5}{2} \\ \\ \rm \: d = \dfrac{40}{2} \\ \\ \boxed{ \boxed{ \rm{d = 20}}}\end{array}}$