这个题是怎么做呢---**Question Stem:** 如图直角三角形 ABC, AB = 12, AC = 5, 则 AD = ? **Translation of Question Stem:** As shown in the figure, in right-angled triangle ABC, AB = 12, AC = 5, then AD = ? **Chart/Diagram Description:** * **Type:** Geometric figure (Triangle). * **Main Elements:** * A triangle ABC. * Vertex A has a right angle symbol, indicating that angle BAC is 90 degrees. * A line segment AD is drawn from vertex A to point D on side BC. * Point D on side BC has a right angle symbol, indicating that AD is perpendicular to BC (AD is the altitude from A to BC). * The length of side AB is labeled as 12. * The length of side AC is labeled as 5. * Points B, D, C are collinear in that order. **Options:** None provided in the image.