生产这道题的解题视频。画出怎么旋转的过程---**Question Stem:** 如图，在Rt △ ABC中，∠ACB = 90°，AC = 4，将斜边AB沿顺时针旋转90°得到线段AD，连接CD，则△ ACD的面积为______． **Diagram Description:** - Type: Geometric figure. - Elements: - Points: A, B, C, D. - Lines: Straight lines forming triangles ABC and ACD. - Triangle ABC: A right triangle with the right angle at C. Vertex C is to the left, A is to the right of C on a horizontal line. B is above C. Line segments are BC, AC, AB. - Triangle ACD: Formed by vertices A, C, and D. Line segments are AC, CD, AD. Point D is to the right and above A. - Relative positions: C, A are on a horizontal line. BC is vertical. AB is the hypotenuse of triangle ABC. AD is obtained by rotating AB clockwise around point A. **Given Information:** - Triangle ABC is a right triangle (Rt △ ABC). - Angle ACB = 90 degrees. - Length of side AC = 4. - Hypotenuse AB is rotated 90 degrees clockwise around point A to obtain line segment AD. - CD is connected. **Question:** Find the area of triangle ACD (△ ACD).