Question

Хэлп
плиз
(2,4,6)
Простите за плохое качество

Answer 1

2) $frac{1}{sin(a)-1}-frac{1}{sin(a)+1}=frac{sin(a)+1-(sin(a)-1)}{sin^{2}(a)-1}=frac{2}{-cos^{2}(a)}$
4) $frac{sin^{2}(O)-1}{cos^{2}(O)-1}+tg(O)ctg(O)=frac{sin^{2}(O)-1}{cos^{2}(O)-1}+1=frac{sin^{2}(O)-1+cos^{2}(O)-1}{cos^{2}(O)-1}=frac{-1}{cos^{2}(O)-1}=frac{-1}{-sin^{2}(O)}=frac{1}{sin^{2}(O)}$
6)$cos^{2}(a)-(ctg^{2}(a)+1)*sin^{2}(a)=cos^{2}(a)-(frac{cos^{2}(a)}{sin^{2}(a)}+1)*sin^{2}(a)=cos^{2}(a)-(cos^{2}(a)+sin^{2}(a))=cos^{2}(a)-1=-sin^{2}(a)$