(2003•内蒙古)如图,已知AD为∠BAC的平分线,且AD=2,AC=
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,∠C=90°,求BC的长及△ABC外接圆直径.
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,BD=3.
(1)请根据下面求cosA的解答过程,在横线上填上适当的结论,使解答正确完整,
∵CD⊥AB,∠ACB=90°∴AC=______cosA,______=AC•cosA
由已知AC=6
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,BD=3,∴
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=AB cosA=(AD+BD)cosA=(
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cosA+3)cosA,设t=cosA,则t>0,且上式可化为
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t
2+______
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(2003•常州)不用计算器求值:
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.
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