The author of the essay studies the transmutation of the triangular theorem of "Five Centers" theorem from the projective viewpoint and puts forward five thoughtful propositions through polarization.
本文用射影观点考察三角形的“五心”定理，通过配极变换推出五个新的命题。
2
In this paper, the existence theorem of midpoint chord of quadratic curve, as well as its proof, is given via methods of projective geometry and polarity principle.