帮我解答并讲解这道数学题---**Question 9:** **Question Stem:** 在四边形 ABCD 中，∠BCD 是钝角，AB=AD，BD 平分∠ABC，若 CD=3, BD =2√6, sin∠DBC=√3/3，求对角线 AC 的长。 (In quadrilateral ABCD, ∠BCD is an obtuse angle, AB=AD, BD bisects ∠ABC. If CD=3, BD =2√6, sin∠DBC=√3/3, find the length of diagonal AC.) **Diagram Description:** * **Type:** Geometric figure (Quadrilateral with a diagonal). * **Elements:** * **Vertices:** Points labeled A, B, C, D. * **Lines:** Line segments connecting A-B, B-C, C-D, D-A (forming the quadrilateral ABCD), and a diagonal connecting B-D. * **Relative Positions:** The figure is a quadrilateral ABCD with diagonal BD drawn. The vertices appear arranged roughly such that B and C are on the bottom line, A and D are on the top line, with BD dividing the quadrilateral. A is left of D, B is left of C. **Other Relevant Text:** None (No options, solutions, hints, or data sources provided).