Point Symmetry about y=x
Two points are symmetric about the line y=x if and only if their coordinates are reversed. Move the blue point into each of the four quadrants and check out the coordinates of the symmetric point.
Box problem (right square prism)
Creating Height and Area Relation in Parallelogram
Vector Equation of a line (3D)
Regular Decagon Magic!
Post shadow, lamp in front
Perp Bis Problem
Exploring Parallel Lines