Find the sum of the interior angles of a decagon.

We know that a decagon has 10 sides.

Therefore, n = 10

Sum of interior angles $=(n-2)\times {180}^o$

$=(10-2)\times {180}^o$

$=8\times {180}^o$

$={1440}^o$

Therefore, the sum of the interior angles of a decagon is ${1440}^o.$