如图,在△ABC中,AB=BC,以AB为直径的⊙O与AC交于点D,过D作DF⊥BC,交AB的延长线于E,F为垂足.(1)求证:直线DE是⊙O的切线;(2)当AB=5,AC=8时,求cosE的值
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![如图,在△ABC中,AB=BC,以AB为直径的⊙O与AC交于点D,过D作DF⊥BC,交AB的延长线于E,F为垂足.(1)求证:直线DE是⊙O的切线;(2)当AB=5,AC=8时,求cosE的值](/uploads/image/z/1519021-37-1.jpg?t=%E5%A6%82%E5%9B%BE%2C%E5%9C%A8%E2%96%B3ABC%E4%B8%AD%2CAB%3DBC%2C%E4%BB%A5AB%E4%B8%BA%E7%9B%B4%E5%BE%84%E7%9A%84%E2%8A%99O%E4%B8%8EAC%E4%BA%A4%E4%BA%8E%E7%82%B9D%2C%E8%BF%87D%E4%BD%9CDF%E2%8A%A5BC%2C%E4%BA%A4AB%E7%9A%84%E5%BB%B6%E9%95%BF%E7%BA%BF%E4%BA%8EE%2CF%E4%B8%BA%E5%9E%82%E8%B6%B3.%281%29%E6%B1%82%E8%AF%81%3A%E7%9B%B4%E7%BA%BFDE%E6%98%AF%E2%8A%99O%E7%9A%84%E5%88%87%E7%BA%BF%3B%EF%BC%882%EF%BC%89%E5%BD%93AB%EF%BC%9D5%2CAC%EF%BC%9D8%E6%97%B6%2C%E6%B1%82cosE%E7%9A%84%E5%80%BC)
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