Links
[1] https://hootsgo.org/?q=node/6550
[2] https://bineeshthomas.wordpress.com/2010/08/26/vedic-maths-sutra-2-nikhilam-navatashcaramam-dashatah-all-from-9-and-the-last-from-10/
[3] http://everything2.com/title/Nikhilam+Navatashcaramam+Dashatah
[4] http://easyvedicmaths.blogspot.in/2010/07/this-is-explanation-to-one-of-16-sutras.html