Coxeter- Exercise 3.4.4
The lines that meet at S seem to be the medians of the triangles ABC and PQR which are all concurrent as seen below.
Copia lui Bisectoare si cerc inscris in triunghi
Half a Glass Please!
Distance between a point and a line
Locus Example 3 (Fixed distance to a line)
Trilinear Pole and Polar
Coxeter- Exercise 3.4.1
Coxeter- Exercise 3.4.2
Coxeter- Exercise 3.4.3