Find the sum of the interior angles of a decagon.

A decagon is a polygon with $10$ sides, so $n=10$.The formula for the sum of the interior angles of an $n$ -sided polygon is:
$$\text{Sum of interior angles}=(n-2)\times 180^{\circ }$$
Substituting $n=10$ into the formula:
$$\text{Sum}=(10-2)\times 180^{\circ }$$
$$\text{Sum}=8\times 180^{\circ }=1440^{\circ }$$