Question

sin a /1 - cos a минус sin a/1+cos a

Answer 1

$displaystyle frac{sin alpha }{1-cos alpha}- frac{sin alpha}{1+cos alpha}= frac{sin alpha(1+cosalpha)-sinalpha(1-cos alpha)}{1-cos^2alpha}=\ \ \ = frac{sinalpha+sinalphacos alpha-sinalpha+sinalphacosalpha}{sin^2alpha} = frac{2sinalphacos alpha}{sin^2alpha} =2ctgalpha$