Question

Quantas diagonais têm um decágono ?

Answer 1

Oi Gabriel

um decágono tem n = 10 lados

d = n*(n - 3)/2
d = 10*7/2 = 70/2 = 35 diagonais

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Answer 2

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