∵ ∠APE＝55°，∴ ∠DPC＝55°．∴ ∠PCD＝∠PCA＝90°－∠DPC ＝35°．∴ ∠ACB＝70°．又∵ ∠AEP＝80°，∴ ∠BAC＝180°－35°－80°＝65°．∴ ∠B＝∠AEP－∠PCD＝80°－35°＝45°．

∠ACB＝70° ∠BAC＝65° ∠B＝45°