C 岛在A岛的南偏东45度方向,B岛在A岛的南偏东80度方向,C岛在B岛的南偏西20度方向,求张角∠ACB的度数

180-(90-45-(90-80))-(180-20-(90-(90-80)))=65
∠CAB=(90-45)-(90-80)=35
∠ABC=180-20-(90-(90-80))=80
∠ACB=180-∠CAB-∠ABC=180-35-80=65