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\u4e09\u89d2\u51fd\u6570\u4e8c\u500d\u89d2\u516c\u5f0f<\/p>\n
\u4e8c\u500d\u89d2\u516c\u5f0f\uff1a<\/p>\n
sin2a=2sinacosa<\/p>\n
tan2a=2tana\/\uff081-tan^2\uff08a\uff09\uff09<\/p>\n
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sin240=sin\uff08270-30\uff09=-cos30\u3002<\/p>\n
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