The following article exhibits a proof of Newton’s inequaltiy. There are many proofs available throughout the internet. However, it is hard to find one which do not uses calculus. This is one which proves directly by induction.
The following article explains aspects of some abstract algebra which is applicable to problems in mathematical olympiad whose (expected, or unexpected) solutions involves concepts of abstract fields, algebraic numbers, or vector spaces.
Gimpse of abstract algebra with a view toward mathemacital olympiads