They have pure elements or a verity of compounds inside.
I’m not sure if its correct but I think it’s focal Ray point
For concave mirrors, some generalizations can be made to simplify ray construction. They are: An incident ray traveling parallel to the principal axis will reflect and pass through the focal point. An incident ray traveling through the focal point will reflect and travel parallel to the principal axis.
It brings a civilized government to backward countries.
Hope this helps! :)
