Coxeter - Figure 1.6 D (right)
A, B, C, and D are any four collinear points. R is a point outside of the line and T, Q, and W are the sections of RA, RB, and RC respectively by a line through D. We can see that ABCD is projective to BADC through this construction.
Cuadrado inscrito en un triángulo
Tangent radius property of a circle
Tangent Line or Tangent
Centroid or Barycenter