图中这道题怎么做？---Extraction Content: Knowledge Point: 考点3 勾股定理的逆定理 (Knowledge Point 3: Converse of the Pythagorean Theorem) Question Stem: 例3 (Example 3) 如图, 在△ABC 中, AB = 3, AC = 4, BC = 5, AD 是△ABC 的角平分线, DE ⊥ AC 于点 E, 则 DE 的长是_______. Given Information: In triangle ABC, AB = 3, AC = 4, BC = 5. AD is the angle bisector of ∠BAC. DE ⊥ AC at point E. Question: Find the length of DE. Diagram Description: Type: Geometric figure (Triangle). Main Elements: - Triangle ABC with vertices labeled A, B, C. A is at the top, B and C are at the bottom. - Side lengths are labeled: AB = 3, AC = 4, BC = 5. - Line segment AD is drawn from vertex A to side BC. It is marked as the angle bisector of ∠BAC by two small arcs inside the angle at A, dividing it into two equal angles. The angles ∠BAD and ∠CAD are also labeled as 45°. - Line segment DE is drawn from point D on BC to side AC, meeting AC at point E. - A right angle symbol is marked at E, indicating DE ⊥ AC. - There is a curved arc connecting points B and C, labeled with 5. - There are text labels "例2题图" and "例3题图" below the triangle, indicating it is the diagram for Example 3. - The number 23 is shown in a cloud shape at the bottom right.