Question

The number of diagonals in a regular octagon is

• A. 20
• B. 18
• C. 14
• D. 21

Answer 1

Answer: (A)

20

No. of diagonals in $n$ - sided polygon $=|n-n_{c_2}|$

$\begin{array}{cc}=& \frac{n(n-3)}{2}\end{array}$

$\therefore$ for octagon, $n=8$

$\therefore$ No of diagonals in octagon $=\frac{8(8-3)}{2}$

$=20$

$\therefore$ Correct option is (A).