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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