在△BCP中,
∵∠PBC+∠P+∠PCB=180°
∴∠P=180°-1/2∠ABC-（∠PCA+∠ACB)
=180°-1/2∠ABC-(1/2∠ACD+∠ACB)
=180°-1/2∠ABC-[1/2(∠A+∠ABC)+∠ACB)
=180°-1/2∠ABC-1/2∠A-1/2∠ABC-∠ACB
=180°-(∠ABC+∠ACB)-1/2∠A
=∠A-1/2∠A
=1/2∠A
=(1/2)α
因为看不到图,只能凭着题目和自己的理解写,过程写得很细,你再看一下吧,应该是对的,希望能帮到你^^