Question

Number of diagonals of a regular octagon is _____

Answer 1

For 'n' sided polygon.

No.of diagonals = $\frac{n(n-3)}{2}$

For octagon, n = 8

$\therefore$ Number of diagonals$=\frac{8(8-3)}{2}$

$=\frac{8\times 5}{2}$

= 20