[m]cos^2(π+ α )=(-cos α)^2=cos^2 α [/m]; [m]cos^2 α=1-sin^2 α =(1-sin α )(1+sin α ) [/m];
[m]cos(\frac{π}{2}- α )=sin α [/m]
[m]\frac{cos^2 α }{1-sin α }=\frac{1-sin^2 α }{1-sin α }=1+sin α [/m]
[m]1+sin α -sin α +tg^2 α =\frac{1}{cos^2 α }[/m] - верно