QA-P21 is the Reflection of QA-P16 (QA-Harmonic Center) in QA-P1 (QA-Centroid) as well as the Midpoint of QA-P5 (Isotomic Center) and QA-P19 (AntiComplement of QA-P16 wrt QA-DT).
(2 p + q + r) (q2 + q r + r2)
-p2 (2 (-p4 + q4 + r4) + (-p2 + q2 + r2)2)
- QA-P21 lies on these QA-lines:
- QA-P21 is the Midpoint of QA-P5 and QA-P19
- QA-P21 is the Involutary Conjugate (see QA-Tf2) of QA-P27.
The 3 QL-versions of QA-P21 are collinear (note Eckart Schmidt).