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本题的解法一般是利用对称法,而关于作法的讨论,各书未有详载。兹将作法上的各种情况和讨论,作系统的叙述,以供参考。如果对题设中的概念详为分析,除了理解所谓“定位”是指给定的三线交成一定的角之外,我们可以将这三线的可能位置分为(1)三线共点和(2)三线两两交成一三角形的两种情况。而在这两种情况之下,给定三线的性质也有可能全为三内角的二等分线,全为三外角的二等分线或三线中其一为内角二等分线,另二为不相邻的两外角二等分线。致于题设中的定点的位置亦可被概括为(a)
The solution to this problem is generally the use of symmetry, and discussion of the practice is not detailed in each book. We will systematically describe the various situations and discussions on the method for reference. If the concept of the title is analyzed in detail, in addition to the understanding that the so-called “positioning” refers to the given three lines intersecting into a certain angle, we can divide the possible positions of the three lines into (1) three lines of common points and (2) ) The two lines of the three lines and two lines form a triangle. In both cases, the nature of a given three-line may also be the bisector of the three-inner angle, the bisector of all three-outer angles, or one of the three lines, which is the inner-division bisector, and the other two Two outer bisectors that are not adjacent to each other. The position of the fixed point in the title can also be summarized as (a)