what is a concave polygon
A concave polygon is defined as a polygon with one or more interior angles greater than 180Â°. It looks sort of like a vertex has been 'pushed in' towards the inside of the polygon. Note that a triangle (3-gon) can never be concave. A concave polygon is the opposite of a convex polygon. See Convex Polygon. In the figure above, drag any of the vertices around with the mouse. Take note of what it takes to make the polygon either convex or concave. Also change the number of sides.