Exercise 30 Page 404

Let's start by recalling the rule for the sum of the measures of the interior angles of a polygon.

Interior Angle Sum of a Polygon

The sum of the measures of the interior angles of a polygon is $(n-2)180,$ where $n$ represents the number of sides.

To find the sum of the measures of the interior angles of an octagon, we will substitute $8$ for $n$ in this expression. The sum of the interior angles of an octagon is $1080^{\circ }.$