3. A novel locus
The problem book [7] is cited by many authors and has motivated many contemporary problems. For example, V. Pambuccian’s work [5] incorporates the axiomatic analysis of a problem found originally in T¸it¸eica’s problem book. Pursuing a similar idea, we now examine what happens to Problem 143, which was originally stated in [7] in the Euclidean context, if we study it in taxicab geometry. Thus, we ask the following:
Question. Consider a circle with center O and radius r in the taxicab plane. Point A is located within the circle. Find the locus of midpoints of all chords of the circle that pass through A.
In Euclidean geometry, the locus is well-known. It is simply a circle with diameter OA. On the other hand, when we consider this same locus problem in the context of taxicab geometry, we quickly see that the locus is not so simple. Figure 1 shows an example of such a locus:
Theorem 2. In general, the locus of midpoints of chords that pass through a point A consists of two straight line segments and two hyperbolic sections, at least one of which contains A.