Question

sin a/1+cos a + sin a/ 1-cos a = 2/sin a тождество

Answer 1

$frac{sinalpha}{1+cosalpha}+frac{sinalpha}{1-cosalpha}=frac{sinalpha-sinalphacosalpha+sinalpha+sinalphacosalpha}{(1+cosalpha)(1-cosalpha)}=frac{2sinalpha}{1-cos^2alpha}=frac{2sinalpha}{sin^2alpha}=frac2{sinalpha}$