Question

quantas diagonais possui o icoságono um polígono de 20 lados

Answer 1

$d = \frac{(n-3).n}{2} \\ \\ d = \frac{(20-3).20}{2} \\ \\ d = \frac{17.20}{2} \\ \\ d = 170$

Answer 2

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

$\Large \text{ \sf{ d = \dfrac{20 \cdot(20 - 3)}{2} } }$

$\Large \text{ \sf{ d = \dfrac{20 \cdot17}{2} } }$

$\Large \text{ \sf{ d = \dfrac{340}{2} } }$

$\Large \text{ \boxed{ \boxed{\sf{ d = 170}}} }$