Real image (such as the images on the right), real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines. A real image occurs where rays converge, whereas a virtual image occurs where rays only "appear" to converge. Real images can be produced by concave mirrors and converging lenses, only if the object is placed further away from the mirror/lens than the focal point and this real image is inverted. As the object approaches the focal point the image approaches infinity, and when the object passes the focal point the image
Concave polygon a convex polygon. As with any simple polygon, the sum of the internal angles of a concave polygon is ("n" − 2) radians, equivalently 180°×("n" − 2), where "n" is the number of sides. It is always possible to partition a concave polygon into a set of convex polygons. A polynomial-time algorithm for finding a decomposition into as few convex polygons as possible is described by . A triangle can never be concave, but there exist concave polygons with "n" sides for any "n" > 3. An example of a concave quadrilateral is the dart. At least one interior angle