The sum of the interior angles of any polygon is always . . .
(180 degrees ) times (2 less than the number of sides in the polygon) .
It doesn't matter whether the polygon is regular, haphazard, convex, or all mangled and squashed etc. The only thing that matters is how many sides it has.
The octagon has 8 sides. So the sum of interior angles is . . .
(180 degrees) times (8 - 2) = (180 x 6) = <em>1,080 degrees</em>
