如图.一艘轮船按箭头所示方向行驶,C处有一灯塔,请你根据图中所标数据求∠ACB的大小.当轮船距离灯塔C最近时,∠ACB是

∠ABC=180°-70°=110°
∠ACB=180°-∠A-∠ABC
=180°-30°-110°
=40°
当轮船距离灯塔C最近时,即BC⊥AB
∴∠ABC=90°
∠ACB=180°-∠A-∠ABC
=180°-30°-90°
=60°