Huhugui

Read a middle school math problem, which is called 胡不归。The purpose is to find shortest travel time between points with different velocity on different segments.

It’s similar to 将军饮马 which looks for shortest distance. But the beauty of 胡不归 is how it construct with sin. The problem is not hard, so I will directly use images from Zhihu

The problem.

The construction

The solution