Reflection of orthocentre in sides lies on the circumcentre
This property can be very deceptive in solving some problems. Better we can know it. Best part is that the property is so obvious and yet not known in general.
The Inscribed Rectangle Problem
Worked Example 7.13
Converse of Pythagorean Theorem
Period 1 Rocket Data
Open Middle Transformations
NS1-04-P2b-CYU1-RQ1 (Exponents with Integer Bases)