Viktor Prasolov - Plane Geometry

RMM 2.pdf

Proofby Mathematical by Mathematical Induction.pdf

A Primer in Combinatorics - Alexander Kheyfits.pdf

Proof by Picture

Mathematical Olympiads

Proofs of the Pythagorean Theorem.pdf

Proofs without Words - Roger B. Nelsen - Ed. 1993.pdf

O Extensie a Inegalitatii Young