⑴sinacosa(tana+cota)=sinacosa（sina/cosa+cosa/sina）=sinacosa*sina/cosa+sinacosa*cosa/sina=sin^2a+cos^2a=1⑵cot^2a(tan^2a-sin^2a)=cot^2a*tan^2a-cot^2a*sin^2a=1-cos^2a*sin^2a/sin^2a=1-cos^2a=sin^2a...