一步一步分析题，把过程生成视频---**Question 20** (12分) **(1)** 如图1, △ABC中, BD、CE分别是∠ABC和∠ACB的角平分线. ① 若∠A=40°, 则∠ABC+∠ACB= 140 °; ∴∠PBC+∠PCB= 70 °; ∴∠BPC= 110 °. ② 若∠A=a, 则∠BPC= 90 + 1/2a (用a表示); **(2)** 如图1, △ABC中, BD、CE分别是∠ABC和∠ACB的角平分线. 若∠A+∠EPD=180°. 求证: BC=BE+CD; **(3)** 如图2, △ABC中, BD、CE分别是∠ABC和∠ACB的角平分线. 当∠A+∠EPD=180°, BP=AC时 ① 求证: BE=EC; ② 直接写出∠A 与∠ABC的数量关系. --- **Chart/Diagram Description:** * **Type:** Geometric figure (Triangle). * **Title:** 图 1 (Figure 1) * **Main Elements:** * Triangle ABC with vertices labeled A, B, C. * Line segment BD starts from vertex B and ends at point D on side AC. * Line segment CE starts from vertex C and ends at point E on side AB. * Point P is the intersection of line segments BD and CE. * BD is indicated as the angle bisector of ∠ABC (by arcs on ∠ABD and ∠DBC). * CE is indicated as the angle bisector of ∠ACB (by arcs on ∠ACE and ∠ECB). * Points E is on AB, and D is on AC. * An angle near vertex A is labeled with 'a' and '40°'. * The angle ∠BPC is labeled with '110°' (handwritten). * The angle ∠EPD is formed by the intersection of BD and CE. * **Labels and Annotations:** Vertices A, B, C, points D, E, P are labeled. Figure is labeled "图 1". Some angle measures or variables (40, a, 110) are written near the corresponding angles. Handwritten text related to calculations (140°, 70°) are also present next to the questions.