49. There are two watches of different sizes, both of which keep accurate time. On their faces, there exists a fixed point , such that the triangle formed by point and the tips of the second hands of the two watches is similar at any given moment.
(Ye Tingyu, Ren Yansong Middle School, Ruian City, Zhejiang, 325202)
Problem 944
Official solution
Proof: Construct a complex plane as shown, let the complex numbers corresponding to points be:
(Where is a parameter)
Assume that a point exists, whose corresponding complex number is , which is the point corresponding to . Then,
(From this, we know that , and the denominator is not zero)
It is independent of the parameter , i.e., point is a fixed point.
Therefore, the fixed point exists.
Note: If the two circles have a common point , and , then the conclusion does not hold. In some cases, similar triangles may degenerate into a set of collinear points.