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(2006•烟台)如图,在矩形ABCD中,DE⊥AC于E,设∠ADE=α,且co...
(2006•烟台)如图,在矩形ABCD中,DE⊥AC于E,设∠ADE=α,且cosα=
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,AB=4,则AD的长为( )
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A.3
B.
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C.
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D.
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