很简单啊,利用半角公式：sinx=2sin(x/2)cos(x/2),cosx=cos(x/2)^2-sin(x/2)^2.化简有：y=(cos(x/2)+sin(x/2))/(cos(x/2)-sin(x/2)))=(1-tan(x/2))/(1+tan(x/2)).然后,令u=tan(x/2),即y=(1-u)/(1+u),再后面,用单调的...