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某天,孙晓琪同学来问我她在解析几何初步的学习过程中遇到的如下试题:题目设直线系M∶xcosθ+(y-2)sinθ=1(0≤θ≤2π),对于下列四个命题:(A)M中所有直线均经过一个定点.(B)存在定点P不在M中的任一条直线上.(C)对于任意整数n(n≥3),存在正n边形,其所有边均在M中的直线上.(D)M中的直线所能围成的正三角形面积都相等.其中真命题的代号是(写出所有真
One day, Sun Xiaoqi students asked me what she encountered in the analysis of the initial learning process the following questions: The subject set the line M: xcosθ + (y-2) sinθ = 1 (0≤θ≤2π), for the following four Proposition: (A) All lines in M go through a fixed point (B) There exists a point P not in any of the straight lines in M. (C) For any integer n (n≥3), there is a positive n-polygon All edges are on a straight line in M. (D) The area of equilateral triangles that a straight line in M can enclose is equal, where the code for the true proposition is (write out all true