Question

How many diagonals are there in an octagon ?

(a) 8 (b) 16 (c) 18 (d) 20

Answer 1

In an octagon, no. of diagonals. $\frac{n(n-3)}{2}=\frac{8(8-3)}{2}=\frac{8\times 5}{2}=20$