Упростите выражение #2, 4, 5, 6

2) [latex] \frac{1}{sin \alpha -1} - \frac{1}{sin \alpha +1} = \frac{sin \alpha +1-sin \alpha +1}{sin^2 \alpha -1} = \frac{2}{-(1-sin^2 \alpha )} =- \frac{2}{cos^2 \alpha } [/latex] 4) [latex] \frac{sin^2Q-1}{cos^2Q-1} +tgQ*ctgQ= \frac{1-sin^2Q}{1-cos^2Q} +1= \frac{cos^2Q}{sin^2Q}+1=ctg^2Q+1= \frac{1}{sin^2Q} [/latex] 5) [latex]tg^2 \alpha (sin^2 \alpha -1)= \frac{sin^2 \alpha }{cos^2 \alpha }*(-(1-sin^2 \alpha ))= - \frac{sin^2 \alpha }{cos^2 \alpha }*cos^2 \alpha =-sin^2 \alpha [/latex] 6) [latex]cos^2 \alpha -(ctg^2 \alpha +1)*sin^2 \alpha=cos^2 \alpha - \frac{1}{sin^2 \alpha } *sin^2 \alpha=cos^2 \alpha -1=[/latex][latex]=-(1-cos^2 \alpha )=-sin^2 \alpha [/latex]