如定义：“平面内到两个定点的距离的差的绝对值等于常数的点的轨迹是双曲线。”

If the definition: "the plane's two fixed-point distance of the poor in absolute terms equal to the constant point of the track is hyperbolic."

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利用二次曲面的不变量判定到一定点和一定平面(定直线)的距离之比为常数的空间点的轨迹。

Make use of constant measure of second order curved face, and judge the space figure that arrive the fixed point and the fixed flat surface (fixed straight line) distance's ratio is a constant.

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