题目出错了吧～应该是(sin3/5π)/(1-cos3/5π)=tan1/5π,证明如下：sin3/5π=2(sin3/10π)(cos3/10π)cos3/5π=1-2(sin3/10π)^2,所以1-cos3/5π=2(sin3/10π)^2(sin3/5π)/(1-cos3/5π)=(cos3/10π)/(sin3/10π)=co...