Question

a soma pra achar as diagonais do octogono

Answer 1

Formula para encontrar o número de diagonais:

Octógono  =  8 lados

D = n . (n - 3) / 2

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

Octógono possui 20 diagonais 

Answer 2

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