Помогите пожалуйста решить 4 примера даю 100 баллов

Решите задачу:

$4)Cos^{2}\alpha*tg^{2} \alpha: (1-Cos^{2}\alpha)=Cos^{2}\alpha *\frac{Sin^{2}\alpha}{Cos^{2}\alpha} :Sin^{2}\alpha=Sin^{2}\alpha*\frac{1}{Sin^{2}\alpha} =1\\\\5)(2+Cos\alpha)(2-Cos\alpha)+(2-Sin\alpha)(2+Sin\alpha)=4-Cos^{2}\alpha +4-Sin^{2}\alpha=8-( Cos^{2}\alpha+Sin^{2}\alpha)=8-1=7\\\\6)\frac{Cost-1}{Sint}*\frac{Cost+1}{Sint}=\frac{Cos^{2}t-1 }{Sin^{2}t}=\frac{-Sin^{2} t}{Sin^{2}t}=-1\\\\7)\frac{1-Sinx}{Cosx}-\frac{Cosx}{1+Sinx}=\frac{(1-Sinx)(1+Sinx)-Cos^{2}x }{Cosx(1+Sinx)}=$ $=\frac{1-Sin^{2}x-Cos^{2}x}{Cosx(1+Sinx)}=\frac{1-(Sin^{2}x+Cos^{2}x)}{Cosx(1+Sinx)} =\frac{1-1}{Cosx(1+Sinx)} =0$