Question

How many diagonals are there in a octagon ?

Answer 1

Find the number of diagonals in an octagon

We know that number of diagonals in a $\mathrm{n}$ sided polygon are $\frac{\mathrm{n}\left(\mathrm{n}-3\right)}{2}$

In an octagon, there are $8$ sides.

So, substitute $\mathrm{n}=8$ in $\frac{\mathrm{n}\left(\mathrm{n}-3\right)}{2}$, we get;

$\frac{8\left(8-3\right)}{2}$

$=$$\frac{8\left(5\right)}{2}$

$=$$4\left(5\right)$

$=$$20$

Hence, there are $20$ diagonals in an octagon.