分两步进行.①先求∠BAC：∠PCD=∠PBC+∠BPC,即1/2∠ACD=40°+1/2∠ABC,∴∠ACD=∠ABC+80°,又∠ACD=∠ABC+∠BAC,∴∠BAC=80°；②证P在∠BAC的外角平分线上：过P分别作PM⊥BC于M,PN⊥AC于N,PQ⊥BA的延长线于Q,由角...