Tick (✓) the correct answer:

Question:

Tick (✓) the correct answer:

How many diagonals are there in an octagon?

(a) 8

(b) 16

(c) 18

(d) 20

Solution:

(d) 20

For a regular $\mathrm{n}$-sided polygon:

Number of diagonals $=: \frac{n(n-3)}{2}$

 

For an octagon:

$n=8$

$\frac{8(8-3)}{2}=\frac{40}{2}=20$

 

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