因为cot(a/2)-tan(a/2)=cos(a/x2)/sin(a/2)-sin(a/2)/cos(a/2)(通分)=[(cos(a/2))^2-(sin(a/2))^2]/[cos(a/2)sin(a/2)] (分子分母同时用倍角公式)=cosa/(1/2*sina)=2cosa/sina所以原式 (cosa)^2/[cot(a/2)-tan (...