How Do You Find the Sum of the Interior Angles of a Polygon?

Squares, pentagons, triangles, polygons. How is it possible to figure out the sum of the interior angles of any of these multi-faceted shapes? There's got to be a formula. Of course there's a formula. That's what algebra is all about, formulas. So watch this video as the instructor illustrates and explains how to figure out the interior angles of these different polygons.