Historical problem from Medieval China

The book The Nine Chapters on the Mathematical Art is an ancient, anonymous Chinese work that gives techniques for solving various practical problems. In 1261, a mathematician named Yang Hui wrote a commentary called "Detailed analysis of the mathematical rules in the Nine Chapters and their reclassifications." This work supposedly contains the "Problem of the Broken Bamboo" which deals with properties of right triangles. If the height of the stalk and of the break are known, the distance from the base of the stalk to the place where the tip touches the ground can be found with the Pythagorean theorem, which was known to them. The angles involved can be found using trigonometry.