Хэлпплиз (2,4,6)Простите за плохое качество

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) $cos^{2}(a)-(ctg^{2}(a)+1)*sin^{2}(a)=cos^{2}(a)-(\frac{cos^{2}(a)}{sin^{2}(a)}+1)*sin^{2}(a)=cos^{2}(a)-(cos^{2}(a)+sin^{2}(a))=cos^{2}(a)-1=-sin^{2}(a)$