Question

Q4) Quantas diagonais tem o octógono? (8 lados)?​

Answer 1

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

Answer 2

$d = \dfrac{n \cdot(n - 3)}{2}$

$d = \dfrac{8 \cdot(8 - 3)}{2}$

$d = \dfrac{8 \cdot5}{2}$

$d = \dfrac{40}{2}$

$d = 20$