讲解这道题---**Textual Information:** 某海港南北方向上有两个海岸观测站A, B, 距离为10海里, 从港口出发的一艘轮船正沿北偏东30°方向匀速航行, 某一时刻在观测站A, B两处分别测得此轮船正好航行到南偏东30°和北偏东75°方向上的C处, 经过0.5时轮船航行到D处, 此时在观测站A处测得轮船在北偏东75°方向上, 求轮船航行的速度。(结果精确到0.1海里/时, 参考数据: $\sqrt{2} \approx 1.414$, $\sqrt{3} \approx 1.732$) * Distance AB: 10 海里 * Time from C to D: 0.5 时 * Desired precision: 精确到0.1海里/时 * Reference data: $\sqrt{2} \approx 1.414$, $\sqrt{3} \approx 1.732$ * Units: 海里, 海里/时 **Chart/Diagram Description:** * **Type:** Geometric diagram illustrating locations and directions related to navigation. * **Main Elements:** * **Points:** Four labeled points A, B, C, and D forming a quadrilateral ABCD. * **Lines:** Straight line segments connecting A to B, A to C, A to D, B to C, and C to D. A vertical line passes through A and extends upwards and downwards, labeled with an upward arrow and "北" (North) at A. A similar vertical line passes through C and extends upwards, labeled with an upward arrow and "北" (North) at C. The line segment AB is vertical, with A positioned above B, implying A is North of B and AB is a North-South line. * **Angles:** * At point A: An angle of 75° is marked between the upward North line and the line segment AD. An angle of 30° is marked between the downward line from A (South direction) and the line segment AC. * At point B: An angle of 75° is marked between the upward line from B (North direction) and the line segment BC. * At point C: An angle of 30° is marked between the upward North line and the line segment CD. * **Labels and Annotations:** Points are labeled A, B, C, D. Direction arrows labeled "北" (North) are shown at A and C. Angle values 75°, 30°, 75°, 30° are marked at the vertices relative to the North/South direction lines. * **Relative Position and Direction:** Points A and B are aligned vertically, with A above B. Point C is positioned to the right and below A, and to the right and above B. Point D is positioned to the right and above A and C. The North lines at A and C are parallel and point upwards. The line AB represents the North-South line between A and B. The marked angles represent bearings or relative directions. * **Legend:** None.