Question

Quantas diagonais tem um octógono ?

Answer 1

20 diagonais
P = n (n-3) /2
P = 8 (8-3) /2
P = 8* 5 /2
P = 40 / 2
P = 20 diagonais espero ter ajudado!

Answer 2

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