Question

número de diagonais de decágono

Answer 1

d= n(n - 3)
__________
        2
d= 10.(10 - 3)
________________
          2
d= 10. 7
________
      2

d= 70
_______
     2

d= 35 

O decágono possui 35 diagonais

Answer 2

$\large\boxed{\begin{array}{l} \rm{d = \dfrac{n \cdot(n - 3)}{2}} \\ \\ \rm{d = \dfrac{10 \cdot(10 - 3)}{2} } \\ \\ \sf{d = \dfrac{10 \cdot7}{2} } \\ \\ \rm{d = \dfrac{70}{2} } \\ \\ \rm{d = 35} \end{array}}$