1.a=180°-b-c b/2+c/2=180°-e 得180°-a=360°-2e a=180°-2e
2.a=180°-b-c 180°-m=180°-(90°-b/2+b)-(90°-c/2+c)=b/2+c/2 a=180°-2m
3.a=180°-b-c 180°-f=180°-b/2-[c+(180°-c)/2]=90°-b/2-c/2 a=360°-2f
4.a=180°-b-c ∠eaf=∠baf-∠bae=(90°-∠b/2-∠c/2 )-(90°-∠b)=∠b/2-∠c/2