Question

determinar i número de diagonais do octógono.

Answer 1

D = n * (n - 3) / 2
D = 8 * (8 - 3) / 2
D = 8 * 5 / 2
D = 40 / 2
D = 20

Espero ter ajudado. Valeu!

Answer 2

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