Titu Andreescu — 106 Geometry Problems (PDF): a vivid tribute to classical problem‑solving
A classic geometry book!
"Let ABC be a triangle with orthocenter H. Let M be the midpoint of BC. Let the circle with diameter AH meet the circumcircle of ABC again at point X. Prove that points X, M, and H are collinear." titu andreescu 106 geometry problems pdf