These problems may have smart solutions with difficult skills. However, I'd like to solve them by brute force: Proof by Exhaustion for number and graph problems; Trigonometric or Analytic Geometry for geometry problems.
- 24 Game Solver: gives you all dissimilar solutions
- Friends and Strangers (Ramsey Number
R(3,3)=6) - Generalized Butterfly theorem
- Desargues's theorem and Pappus's theorem: Cartesian and Homogeneous coordinates
- Menelaus's theorem and Ceva's theorem by Homogeneous coordinates
- Pascal's theorem, Brianchon's theorem and Braikenridge-Maclaurin theorem
- Steiner Conic
- Radical Center and Monge's theorem
- Symmedian and Isogonal Conjugate
- Euler Line and Incenter
- Feuerbach point
- Contest problems
- Solid geometry
Problems in How to Solve It by G. Pólya