Question

(tg a + ctg a) (1+ cos a) (1- cos a)=

Answer 1

$(tg a + ctg a) (1+ cos a) (1- cos a)=( frac{sina}{cosa}+ frac{cosa}{sina})(1-cos^2a)=$$=frac{sin^2a+cos^2a}{cosa*sina}*sin^2a=frac{1}{cosa*sina}*sin^2a= frac{sina}{cosa}=tga$