Question

60 pontos! 
Calcule a soma dos angulos internos dos seguintes poligonos :
       -eneagono

       -decagono
  
      - icosagono

Answer 1

$a)\;S_i=(n-2)\times180=(9-2)\times180=7\times180=1260^{\circ}\\\\ b)\;S_i=(n-2)\times180=(10-2)\times180=8\times180=1440^{\circ}\\\\ c)\;S_i=(n-2)\times180=(20-2)\times180=18\times180=3240^{\circ}$