tan9°-tan27°-tan63°+tan81=?(不用和差化积)
问题描述：
tan9°-tan27°-tan63°+tan81=?(不用和差化积)
答
tan9°-tan27°-tan63°+tan81 = tg9 + ctg9 - (tg27 + ctg27 ) = sin9/cos9 + cos9/sin9 - (sin27/cos27 + cos27/sin27) = 1/(sin9cos9) - 1/(sin27cos27) =2 * [1/sin18 - 1/sin54] = 2 * [1/sin18 - 1/cos36] =2 ...