The number of diagonals that can be drawn by joining the vertices of an octagon is
Question:

The number of diagonals that can be drawn by joining the vertices of an octagon is

(a) 20

(b) 28

(c) 8

(d) 16

Solution:

(a) 20

An octagon has 8 vertices. 

The number of diagonals of a polygon is given by $\frac{n(n-3)}{2}$

$\therefore$ Number of diagonals of an octagon $=\frac{8(8-3)}{2}=20$

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