二倍角与半角的正弦、余弦和正切的题~

(1+cos(a)-sin(a))/(1-cos(a)-sin(a))+(1-cos(a)-sin(a))/(1+cos(a)-sin(a))首先通分,公分母为:(1-sin(a))^2-(cos(a))^2=1-2*sin(a)+(sin(a))^2-(cos(a))^2=2*(sin(a))^2-2*sin(a)=2*sin(a)*(sin(a)-1)第一项分子为:(1+cos(a)-sin(a))*(1+cos(a)-sin(a))=2-2*sin(a)+2*cos(a)-2*sin(a)*cos(a)第二项分子为:(1-cos(a)-sin(a))*(1-cos(a)-sin(a))=2-2*sin(a)-2*cos(a)+2*sin(a)*cos(a)两项相加为:4-4*sin(a)=-4*(sin(a)-1)再除以分母为:-2/(sin(a))即最终化简结果。