Помогите решить номер 304 а

[latex]( \frac{1}{1+ ctg^{2} \ \alpha } + cos^{2} \alpha )* tg^{2} \alpha = ( \frac{1}{1+ \frac{cos^{2} \alpha}{ sin^{2} \alpha } } + cos^{2} \alpha )* tg^{2} \alpha =[/latex] [latex]( \frac{1}{ \frac{cos^{2} \alpha+sin^{2} \alpha}{sin^{2} \alpha} } + cos^{2} \alpha )* tg^{2} \alpha = ( \frac{ sin^{2} \alpha }{ cos^{2} \alpha+sin^{2} } + cos^{2} \alpha )* tg^{2} \alpha=[/latex][latex](sin^{2} \alpha+cos^{2} \alpha )* tg^{2} \alpha =tg^{2} \alpha [/latex]