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    • 求证：cosx •cos2x•cos4x= sin8x 8sinx ．

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    第1个回答  2022-07-31
    证明：由倍角公式sin2x=2sinxcosx，故sin8x=2sin4xcos4x=4sin2xcos2xcos4x=8sinxcosxcos2xcos4x，所以sin8x8sinx．=8sinxcosxcos2xcos4x8sinx=cosx•cos2x•cos4x，故cosx•cos2x•cos4x=sin8x8sinx．得证．...
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