求值.(cos15°*sin9°+sin6°)/(sin15°*sin9°-cos6°)

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求值.
(cos15°*sin9°+sin6°)/(sin15°*sin9°-cos6°)

(cos15°sin9°+sin6°)/(sin15°sin9°-cos6°)
=[cos15sin9+sin(15-9)]/[sin15sin9-(cos15-9)]
=(cos15sin9+sin15cos9-cos15sin9)/(sin15sin9-cos15cos9-sin15sin9)
=(sin15cos9)/(-cos15cos9)
=-tan15
=-sin30/(1+cos30)=根号3 -2.