Try forming a perfect polygon by extending the un-equal side as if it were equal and then use some trigonometry to get the missing angle.
Hope someone can help, I can't find anything online.
I need to know if there's a way to find the interior angles of an irregular convex polygon, all of whose sides but one have the same length and the same angle between them, when you know only the lengths of all sides. Or a series of equations specific to the number of sides would work as well.
Thanks in advance.
You might want to divide the polygon into triangles and again use trig properties to get the angles (most of the stuff in geometry uses these sorts of decompositions for your problems with polygons).