[tex]\text{tg}^2\ \alpha+1=\frac{\sin^2\alpha}{\cos^2\alpha}+1=\frac{\sin^2\alpha}{\cos^2\alpha}+\frac{\cos^2\alpha}{\cos^2\alpha}=\frac{\sin^2\alpha+\cos^2\alpha}{\cos^2\alpha}=\frac{1}{\cos^2\alpha}[/tex]
Odp: B
