帮我解出这道题---**Extraction Content:** **Geometric Figure Description:** * Type: Geometric diagram. * Main Elements: * A square ABCD. * Vertices are labeled A (top right), B (top left), C (bottom left), D (bottom right). * Point P is located inside the square. * Point E is located on the side AD. * Line segments forming the sides of the square (AB, BC, CD, DA) are drawn. * Line segments connecting the vertices diagonally (AC, BD) are drawn. * Line segments connecting point P to vertices A, B, C, and D are drawn (PA, PB, PC, PD). * A line segment PE is drawn. * A line segment BE is drawn. **Textual Information:** * **Question Stem:** P为正方形ABCD内一点, E为AD中点, 求当PA+PB+PC+PD+PE最小时, cos∠ABP-cos∠BAP的值