pèi jí ㄆㄟˋ ㄐㄧˊ 配极（配极）
文章利用射影几何方法及配极原理给出二次曲线中点弦存在性定理的证明。
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.
并进一步在欧氏平面上提出了一系列对偶命题和阐述标准配极对应的应用。
Moreover, we point out a series of the dual propositions and explain the application of the canonical polarizing correspondence in Euclidean plane.
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。
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.
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