二次曲线中点弦存在性问题的探讨，对二次曲线的研究有着及其重要的意义。
Problems about the existence of midpoint chord of quadratic curve is worthy of discussing in the study of the theories about quadratic curve.
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.
直线被圆锥曲线截得弦的中点问题，是解析几何的重点和难点。
The problems about the midpoints of the chords cut by the taper curve are the most critical and difficult in analytic geometry problems.
在准备拨弦时你需要伸展这个关节，而保持大关节在运动范围之中的中点位置。
Preparation for a stroke requires that you extend the finger at the middle joint, while keeping the large joint at about the middle point of the limits of its range of motion.
在准备拨弦时你需要伸展这个关节，而保持大关节在运动范围之中的中点位置。
Preparation for a stroke requires that you extend the finger at the middle joint, while keeping the large joint at about the middle point of the limits of its range of motion.
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