Question

In a polygon the number of diagonals is 54. The number of sides of the polygon is

• A. 10
• B. 12
• C. 9
• D. none of these

Answer 1

The correct option is B 12

We know,
Number of diagonal in a polygon having $n$ side is $=\frac{n(n-3)}{2}=54$ (given)
$\Rightarrow n(n-3)=54\times 2=108=12\cdot 9\Rightarrow n=12$