题目是否错了?由sin1/[cos(n-1)*cosn]+tan(n-1)=[sin1+sin(n-1)*cosn]/[cosn*cos(n-1)]={sin1[(sinn)^2+(cosn)^2]+sinn*cos1*cosn-sin1*cosn*cosn}/[cosn*cos(n-1)]=[sinn(cos1*cosn+sin1*sinn)]/[cosn*cos(n-1)]=si...