Question

sin a/1+cos a + sin a/1-cos a

Answer 1

sin a /(1 - cos a) - sin a/(1+cos a)=(sin a(1+cos a)-sin a(1-cos a))/(1 - cos a)(1+cos a)=sin a(1+cos a-1+cos a)/(1 - cos a)(1+cos a)=sin a *cos^2 a/1-cos^2 a=sin a *cos^2 a/sin^2 a=cos^2 a/sin a=ctg^2 a*sin a