Question

How many diagonals can be drawn in a (i) decagon (ii) icosagon

Answer 1

(1) Decagon : Number of digonals

$\Rightarrow \frac{n(n-3)}{2}\{n⟶sides\}\Rightarrow \frac{10\times 7}{2}\Rightarrow 35$

Number of digonals is $35$

(2) Icosagon : Number of digonals

$\Rightarrow \frac{n(n-3)}{2}\{n⟶sides\}\Rightarrow \frac{20\times 17}{2}\Rightarrow 170$

Number of digonals is $170$