题目已知⊙O\odot O⊙O的半径为555,四边形ABCDABCDABCD内接于⊙O\odot O⊙O,∠BAC=∠DAC=45∘\angle BAC=\angle DAC=45^{\circ}∠BAC=∠DAC=45∘.(Ⅰ)(Ⅰ)(Ⅰ)如图①,若AB=6AB=6AB=6,求弦ADADAD和BCBCBC的长；(Ⅱ)(Ⅱ)(Ⅱ)如图②,连接OAOAOA,若∠ACB=2∠ACD\angle ACB=2\angle ACD∠ACB=2∠ACD,求弦ABABAB的长和∠OAC\angle OAC∠OAC的大小.知识点：切线的性质章节：图形的性质 / 圆
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