原式＝tan9-tan27-tan63+tan81＝tan9-tan27-cot27+cot9＝sin9/cos9 +cos9/sin9-(sin27/cos27+cos27/sin27)＝1/sin9cos9-1/sin27cos27＝2/sin18-2/sin54＝2(sin54-sin18)/sin18sin54＝4cos36sin18/sin18sin54＝4sin54...