南开大学数学系所编《空间解析几何引论》教材中的习题,武汉师范学院孝感分院数学系编了一本《习题解答》,其中第四章第九节习题2的解答是错误的。习题2的内容是:“已知动点到两相错直线间的距离相等,求动点轨迹。”《习题解答》的结论是“轨迹为两条相交直线。”而正确答案应是“轨迹为一双曲抛物面”。我在一九八0年的教学中,发现了习题解答中的错误。 Nankai University, Department of Mathematics, “Space Analysis Geometry Introduction” textbook exercises, Wuhan Normal College Xiaogan Branch Department of Mathematics compiled a “solution to the problem,” which Chapter IX of Exercise 2 is wrong. Exercise 2 reads: “Known moving point to the distance between two straight lines equal to the point trajectory.” “Exercise Solution” concluded that “the trajectory of two intersecting lines.” And the correct answer should be “trajectory Parabolic for a double song. ” In my teaching in 1980, I found a mistake in the solution to the problem.