1）因为∠BCA为圆周角,因此∠BCA=90度 => BC平行OD => ∠BDO = ∠CBD因为∠BCA=90度,∠BAC=30度,因此∠CBA=60度因为OB = OD,因此△OBD为等腰△,∠BDO = ∠BAC=> ∠BDO = ∠BAC = ∠CBD = ½∠CBA = 30度2）Rt△A...