Question

quantos diagonais tem um octogono

Answer 1

Octógono = 8 lados.

diagonais = n (n-3)/2
diagonais = 8*(8-3)/2
diagonais = 4*5
diagonais = 20

Answer 2

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